E:\bj\nsc\SWEET-910801-920731.doc 1
行政院國家科學委員會補助專題研究計畫
□ 成 果 報 告
;
期中進度報告
（瞭望台灣海峽環境與生態－總計畫及子計畫一：
台灣海峽之水團組成、流通量與聖嬰現象（II）（1/2）
計畫類別：
□
個別型計畫 ; 整合型計畫
計畫編號：NSC 91－2166－M－110－013－
執行期間： 91 年 8 月 1 日至 92 年 7 月 31 日
計畫主持人：陳鎮東教授
共同主持人：劉倬騰教授、白書禎教授
計畫參與人員： 羅立章、邢麗玉、候偉萍、蔡長利、郭富雯、王冰潔、
許志宏、陳建華
成果報告類型(依經費核定清單規定繳交)：;精簡報告 □完整報告
本成果報告包括以下應繳交之附件：
□赴國外出差或研習心得報告一份
□赴大陸地區出差或研習心得報告一份
□出席國際學術會議心得報告及發表之論文各一份
□國際合作研究計畫國外研究報告書一份
處理方式: 除產學合作研究計畫、提升產業技術及人才培育研究計畫、
列管計畫及下列情形者外，得立即公開查詢
□ 涉及專利或其他智慧財產權， □一年□ 二年後可公開查詢
執行單位: 中山大學海洋地質及化學研究所
中 華 民 國 九十二 年 五 月 二十一 日
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2
本計畫自九十一年八月至今，共發表
（一） 論文如下：
SCI
1 Saino, T., A. Bychkov, C.T.A. Chen and P.J. Harrison The Joint Global
Ocean Flux Study in the North Pacific, Deep-Sea Research II, 49, 5297-5301,
2002.
（附件1）
SCI
2 Chen, C.T.A. Shelf vs. dissolution generated alkalinity above the chemical
lysocline in the North Pacific, Deep-Sea Research II, 49, 5365-5375, 2002.
（附件2）
3 Hong, G.H., H.H. Kremer, J. Pacyna, C.T.A. Chen, H. Behrendt, W.
Salomons and J.I. Marshall Crossland, East Asia Basins: LOICZ Global
Change Assessment and Synthesis of River Catchment-Coastal Sea
Interaction and Human Dimensions, LOICZ Reports and Studies, No. 26,
262pp, 2002.
4 Chen, C.T.A. and J.T. Liu Island based catchments: the Taiwan example, in
Hong, G.H., H.H. Kremer, J. Pacyna, C.T.A. Chen, H. Behrendt, W.
Salomons and J.I. Marshall Crossland, East Asia Basins: LOICZ Global
Change Assessment and Synthesis of River Catchment-Coastal Sea
Interaction and Human Dimensions, LOICZ Reports and Studies, No. 26, pp
170-176, 2002.
5 Chen, C.T.A. Dams may impact fisheries even beyond the estuaries, in
Hong, G.H., H.H. Kremer, J. Pacyna, C.T.A. Chen, H. Behrendt, W.
Salomons and J.I. Marshall Crossland, East Asia Basins: LOICZ Global
Change Assessment and Synthesis of River Catchment-Coastal Sea
Interaction and Human Dimensions, LOICZ Reports and Studies No. 26, pp
177-178, 2002.
6 Chen, C.T.A., S.L. Wang and B.J. Wang Nutrient budgets for the South
China Sea basin, in “Marine Environment: The Past, Present and Future”, ed.
C.T.A. Chen, Fuwen Press, Kaohsiung, pp 303-344, 2002.
SCI
7 Hong, G. H. and C. T. A. Chen Aragonitic pteropod flux to the interior of
the East Sea (Japan Sea), Terrestrial, Atmospheric and Oceanic Sciences, 13,
205-210, 2002.
8 Chen, C.T.A. The impact of dams on fisheries: Case of the Three Gorges
Dam, Chapter 16, in “Challenges of a Changing Earth”, eds. W. Steffen, J.
Jager, D.J. Carson and C. Bradshaw, Springer, Berlin, 97-99, 2002.
SCI
9 Chen, C.T.A. Rare northward flow in the Taiwan Strait in winter: A note,
Continental Shelf Research, 23, 387-391, 2003.
（附件3）
SCI
10Chen C.T.A. New vs. export production on the continental shelf, Deep-Sea
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3
SCI
11Chen, C.T.A., C.T. Liu, W.S. Chuang, Y.C. Yang, F.K. Shiah, T.Y. Tang and
S.W. Chung Enhanced buoyancy and hence upwelling of subsurface
Kuroshio waters after a typhoon in the southern East China Sea, Journal of
Marine System, accepted, 2003.
12Chen, C.T.A., K.K. Liu and R. MacDonald Continental margin exchanges,
in “Ocean Biogeochemistry: a JGOFS Synthesis”, ed. M.J.R. Fasham,
Springer, pp53-97, 2003.
（二） 自九十一年八月至今，共參加航次如下：
航次
日期
OR2-871
91 年
8 月
1~2 日
OR1-653
91 年
8 月 7~10 日
OR2-1034
91 年 10 月
15~16
日
OR3-824
91 年 11 月
4~7 日
OR1-672
92 年
1 月
13~17
日
OR3-851
92 年
3 月
4~7 日
OR2-1082
92 年
4 月
15~16
日
（三） 已採購離子層析儀，正試用中。
Deep-Sea Research II 49 (2002) 5297–5301
Overview
The Joint Global Ocean Flux Study in the North Pacific
Toshiro Saino
a,*, Alexander Bychkov
b, Chen-Tung Arthur Chen
c,
Paul J. Harrison
d,1aHydrospheric Atmospheric Research Center, Nagoya University, Nagoya 464-8601, Japan bNorth Pacific Marine Science Organization, c/o Institute of Ocean Sciences, Sidney, BC, Canada V8L 4B2 cInstitute of Marine Geology and Chemistry, National Sun Yat-Sen University, Kaohsiung 804, Taiwan, ROC
dSchool of Earth and Ocean Sciences, University of British Columbia, Vancouver, BC, Canada V6T 1Z4
Abstract
This volume of DSR II is dedicated to the Joint Global Ocean Flux Study (JGOFS) North Pacific Process Study (NPPS), coordinated by the JGOFS North Pacific Task Team. Following the studies conducted by Canadian JGOFS in the eastern subarctic Pacific, the JGOFS NPPS focused mainly on the western subarctic Pacific. The goals of the JGOFS NPPS were to quantify CO2drawdown by physical and biological pumps in the northern North Pacific by
identifying and studying the regional, seasonal to inter-annual variations of the key processes, and to understand their regulating mechanisms. The NPPS was composed mainly of Japanese programs conducting extensive surveys, intensive biogeochemical process studies, time-series observations at station KNOT at 441N, 1551E, ocean color satellite observations, and modeling. A total of 27 papers included in this volume cover CO2 intrusion to the intermediate
waters, biogeochemical time-series observations at station KNOT, vertical fluxes in the water column, and the east–west Pacific Ocean comparison of ecosystems and biogeochemical regimes.
r2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
The North Pacific can be viewed as the largest global estuary in which a steep halocline at 100– 120 m depth separates the surface from deeper waters. Nutrient concentrations in deep waters are the highest in the global ocean because it is the terminal region for the abyssal circulation. This setting provides a unique situation in the northern
North Pacific where high concentrations of nu-trients are located below the shallow halocline with very large concentration gradients with depth. This region is also known as a region of intense winter cooling due to air–sea interactions with the monsoonal wind, in that the winter cooling takes place to a greater extent in the western subarctic Pacific. The regional difference is also noted in the ecosystem structure in the eastern and western subarctic Pacific. It is well documented that the spring blooms, mainly consisting of diatoms, occur only in the western part of the subarctic Pacific. The intense air–sea interactions in winter cause
CO2exchange that needs to be evaluated
quanti-tatively in the context of the global carbon cycle.
*Corresponding author. Tel.: 52-789-3487; fax: +81-52-789-5508.
E-mail address:tsaino@ihas.nagoya-u.ac.jp (T. Saino).
1Department of Biology, Hong Kong University of Science
and Technology, Clear Water Bay, Kowloon, Hong Kong
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Considering this background, Joint Global Ocean Flux Study (JGOFS) Japan (Chair: Nobu-hiko Handa) proposed a process study in the North Pacific at the JGOFS Scientific Steering Committee held in Bad M.unstreifel in April 1996. The JGOFS SSC responded by establishing the North Pacific Task Team (NPTT) and by provid-ing Terms of Reference (TOR). The scientific objectives of the TOR were as follows:
The primary issues to be addressed by the NPTT are the quantification of the
biogeo-chemical cycles of carbon and associated
elements in the North Pacific Ocean and its marginal seas.
The specific objectives are:
(1) to assess the efficiency of physical and biological pumps, and their seasonal changes for differentdomains of the North Pacific and the adjacent marginal seas, including the effects of sea ice;
(2) to study the formation and spreading of the intermediate water, and its implication for lateral flux of dissolved inorganic, dissolved organic and particulate matter;
(3) to investigate and ultimately to enhance our
understanding of air–sea fluxes of CO2 and
other atmospherically reactive gases that lead to predictions of the role of the North Pacific as a source and/or sink of CO2in
collabora-tion with IGAC;
(4) to understand the role of iron in maintaining the northern North Pacific as a high nutrient– low chlorophyll region; and
(5) to clarify the mechanism(s) controlling the transport of nutrients into the euphotic zone of the subtropical Pacific Ocean.
The NPTT (Co-Chairs: Alexander Bychkov and Toshiro Saino) reviewed the TOR in the Task Team meetings in 1996 and 1997, and determined the goals of the NPPS.
Those were:
To quantify CO2 drawdown by physical
and biological pumps in the northern North Pacific by identifying and studying the regional, seasonal–interannual variation of the key
pro-cesses, and to understand their regulating
mechanisms.
The objective questions to be answered in the NPPS were listed as:
* Whatis the amountof CO
2 absorbed by the
North Pacific Intermediate Water?
* Does the amount vary with long-term,
large-scale physical forcing?
* Whatis the amountof CO
2 absorbed by the
biological pump?
* What is the regional and temporal variability of
the efficiency of the biological pump?
* What controls the efficiency of the biological
pump: iron input, community structure of lower trophic level organisms?
* Why do blooms occur in the western sub-arctic
Pacific, not in the eastern sub-arctic Pacific? To answer these questions, the NPTT coordi-nated the NPPS and its intensive phase was from July 1998 through February 2000. With comple-tion of the NPPS, the NPTT was renamed as the North Pacific Synthesis Group in the fall of 2000.
JGOFS Japan putmostof their effortin
establishing a time-series station in the western subarctic Pacific. From the very beginning of the NPTT there was a strong desire for a time-series station, but due chiefly to the logistic problems, it was thought to be very difficult without designated funding. Fortunately, the plan proposed by Yukihiro Nojiri was approved as one of the projects of Core Research for Evolutional Science and Technology (CREST) supported by Japan Science and Technology Corporation from 1997 through 2002, and the KNOT (Kyodo—coopera-tive in Japanese—North Pacific Ocean Time Series) station was established.
Fig. 1 shows the organizational structure of the JGOFS NPPS. There were 5 componentactivities with data management as a framework activity. The extensive observations included the SubArctic Gyre Experiment(SAGE), a post-WOCE program supported by the Science and Technology Agency, and the Canada–Japan Cargo Ship monitoring program using the M/S Skaugran. One of the objectives of the SAGE program, relevant to the JGOFS NPPS, was the formation, transformation, and transport of the North Pacific Intermediate Water (NPIW). The Skaugran monitoring pro-gram provided comprehensive maps of the sea
Overview / Deep-Sea Research II 49 (2002) 5297–5301 5298
surface pCO2and nutrients with an unprecedented
coverage in temporal and spatial scales in the study region. The time-series station KNOT was in operation from June 1998, and was occupied 20 times by February 2000, the end of intensive observation phase of NPPS. The research vessels that made observations at station KNOT were the Hokusei maru of Hokkaido University, the Mirai of Japan Marine Science and Technology Center, the Bosei maru of Tokai University, and the Hakuho maru of the University of Tokyo. In addition to KNOT, the Japan Fisheries Agency has maintained, from the early 90s, a monitoring
line running from the eastcoastof Hokkaido
Island in the southeastward direction, crossing the Oyashio, a cold western boundary current of the western subarctic gyre. The intensive observations and shipboard experiments on biogeochemical processes were also conducted on cruises to the northern North Pacific, and were not limited to the western subarctic Pacific. In addition to the ships listed above, the Hakurei maru I and II, supported by the Ministry of International Trade and Industry, were engaged in the Western Pacific
Environmental Study on CO2 Ocean
Sequestra-tion for MitigaSequestra-tion of Climate Change (WEST-COSMIC) project. Another CREST project was established in the Sea of Okhotsk (Masaaki Wakatsuchi), where sea ice is an important
component of the climate system and the source water of NPIW.
2. Overview
Papers in this volume are organized by topic. The firstgroup of papers deals with CO2intrusion
into the North Pacific. The temporal and spatial variability of sea-surface pCO2and nutrients in the
entire transects of northern North Pacific, as observed by the Skaugran monitoring program, showed that the whole region was in a high-nutrient low-chlorophyll condition, and the
varia-bility in pCO2 and nutrients was higher in the
western subarctic (Zeng et al. and Wong et al.). The latter implies that either the physical and/or biological pump activity is larger in the western subarctic Pacific. Kumamoto et al. showed clearly, based on the observed change of bomb radio-carbon distribution patterns during GEOSECS and JGOFS, that CO2is actively sequestered in the
western subarctic and transported to the east with the NPIW. The quantitative estimate of the formation and transport of NPIW in the western subarctic (Hiroe et al.) confirmed this view. The coastal regions around the North Pacific are also
important in sequestering CO2 into the ocean.
Chen suggested that the anaerobic processes in the
Remote Sensing ADEOS-OCTS/NSCAT SeaWiFS QuickSCAT Intensive Obs. Mirai, Hakuho Hakurei I, II Hokusei, Bosei CREST-OKHOTSK Time Series CREST-KNOT JFA-ALine US-HOT Canada-Papa Extensive Obs. SAGE Skaugran Modeling JGOFS-GLOBEC Data Management:JODC
Fig. 1. Organizational structure of the JGOFS North Pacific Process Study. This depicts only the Japanese components and does not include international activities of participating countries. After completion of the intensive phase of observation, this structure is maintained in the synthesis phase. The Japan Oceanographic Data Center hosts the JGOFS Japan Data Management Office.
shelf sediments generate alkalinity, in addition to calcium carbonate dissolution, and are globally important for sequestration of CO2in the shallow
waters.
A large seasonal variability in parameters related to biological processes is characteristic of the western subarctic Pacific. Detailed seasonal variability in the western subarctic Pacific was first
depicted by the time-series station KNOT on CO2
and nutrients (Tsurushima et al.), phytoplankton biomass and primary productivity (Imai et al.), abundance of picoplankton and bacteria (Liu
etal.), and phytoplankton >10 mm (Mochizuki
etal.). The large variability in CO2 and nutrients
was attributed to the biological production from spring to fall and strong vertical mixing in winter. Phytoplankton biomass in chlorophyll a showed a peak in spring due to an increased diatom population, but remained at a relatively constant low level during the rest of the seasons. Primary productivity showed a 10-fold variation, unlike that at Station P in the eastern subarctic Pacific, with the peak in spring, but the level of the primary productivity was lower than that of Station P. The picophytoplankton abundance indicated a clear seasonal pattern with a peak after the spring diatom bloom in late June to August. The abundance of heterotrophic bacteria also showed a seasonal pattern closely related to the picoplankton biomass. Among phytoplankton >10 mm in size, diatoms were the major constitu-ent at station KNOT. It was noted that the
dominantdiatom species was Thalassiosira at
station KNOT, whereas that at Station P esti-mated from the samples collected by sediment traps was Rhizosolenia. A one-dimensional ecosys-tem model, having 15 compartments including two phytoplankton and three zooplankton categories, was capable of reproducing the variability of nutrients and the water column-integrated chlor-ophyll a. The temporal pattern of variability of primary productivity was reproduced by the model, but the magnitude of the primary produc-tivity was overestimated by more than 50% (Fujii et al.). Saito et al. reported on another time-series observations along the A-line in Oyashio waters. The variability in nutrient concentrations along the A-line was much larger than at station KNOT.
The summertime nitrate and silicate were nearly depleted. They pointed out that the mechanism responsible for the termination of the spring phytoplankton bloom, may be associated with either phytoplankton limitation by silicate during the bloom and/or grazing by zooplankton. In addition, taking advantage of the long-term monitoring data sets obtained by the Japan Meteorological Agency in the subarctic and subtropical western North Pacific, Limsakul et al. documented climatologically averaged seasonal variability in the lower trophic level parameters in both regions. Compared to subtropical waters, they characterized the western subarctic Oyashio waters by their high variability, shallow pycno-cline, rich nutrients in the euphotic layer, and the co-occurrence of peaks of phytoplankton and meso-zooplankton abundances. It is of interest to note that the variability in nitrate encountered at station KNOT during 1998–2000 was almost the same as the climatological average in the Oyashio waters. The difference in the lower trophic environment in shallow waters in the subarctic and subtropical western Pacific can be noted in the deep water as clearly shown by Yamaguchi etal.
A large spatial variability was also noted during the NPPS on several cruises to the western subarctic Pacific. Murata et al. conducted detailed surveys of the spring diatom bloom in the vicinity
of station KNOT in May 1999. The pCO2 was
reduced to less than 200 matom in a bloom whose
chlorophyll concentration was ca. 10 mg m3.
They attributed this drawdown of CO2 to the
uptake by phytoplankton (mainly diatoms) and estimated the net community productivity of >1 g C m2d1. Quantitative estimates of the diatom bloom are thus crucial in estimating the biological pump in the western subarctic Pacific. Sasaoka et al. reported on the temporal and spatial variability of chlorophyll a in the western subarctic Pacific from 1997 to 1999. Based on the monthly composite images of chlorophyll a, sea-surface temperature, and sea-surface wind, they were able to show why a high concentration of chlorophyll a appeared near the center of the western subarctic gyre (501N, 1651E) in the fall of 1998 when El Ni*no took place.
Overview / Deep-Sea Research II 49 (2002) 5297–5301 5300
The vertical flux of carbon and nutrients through the halocline in the western subarctic was estimated by model calculations assuming a steady state on an annual basis (Andereev et al.). Their estimate agreed well with sediment trap experiments conducted in the region (Honda et al.). Honda et al. showed that the ratios of opal/CaCO3
and organic carbon/inorganic carbon in the trapped materials were amongst the highest reported values in the world’s oceans, and the export ratio, defined as the ratio of the organic carbon flux to depth, to the primary productivity in shallow depth, was about 5% at 1000 m. This value is also the highest among those reported so
far. Kuroyanagi etal. reported on the seasonal
variability of planktonic foraminifera observed in the same samples. Kawahata et al. reviewed the results of their sediment trap experiments along a meridional transect between 461N and 351S and an equatorial longitudinal transect between 1351E and 1751E in the Pacific. They also noted that the increase in organic matter and biogenic opal fluxes was generally associated with higher organic-carbon/inorganic-carbon ratios. Shin et al. re-ported on the other sediment trap experiments at
401250N, 1441280E. They also pointed out the
importance of diatoms in vertical flux and proposed that polyunsaturated fatty acids could be a good measure to estimate the diatom contribution to the vertical flux.
The important aspect of the NPPS is the east– west difference in the ecosystems and hence the biogeochemical regimes. Suzuki etal. showed that the phytoplankton assemblages, estimated by chemotaxonomic analysis of pigment composition, in the eastern and western subarctic gyres were
similar in that small phytoflagellates were
pre-dominantand the microbial loop prevailed. It
should be noted that their observation was made under the non-bloom conditions in the summer of 1999. In the analysis of the time-series data from sediment trap experiments, Wong and Crawford observed significant correlations between the monthly anomalies of particulate inorganic and organic carbon (PIC and POC) fluxes and the equatorial sea-surface temperature anomaly. As the oceanic sequestration of CO2is sensitive to the
flux ratio of PIC/POC, their finding has profound implication in understanding the relationship between climate variability and carbon cycle in the ocean. Wong et al. also analyzed time-series data at Station P to examine whether or not the C=N ratios in uptake and regeneration processes were consistent with the Redfield ratio, and found that, after correction for the calcification, the C=N ratio for uptake and regeneration were close to the Redfield ratio. This also highlighted the impor-tance of calcification in the eastern subarctic
Pacific. Denman and Pe*na reported results of
model experiments on the responses of ecosystems in the eastern subarctic Pacific to the various scenarios of global climate change such as increased ocean temperature, and availability of iron. An intriguing result was seen by removing iron limitation from phytoplankton growth, where an increase in standing stock was observed for microzooplankton, but not for phytoplankton. From the Line-P observations, seasonal variability in dissolved organic nitrogen (Wong et al.), bacterial biomass and productivity (Sherry et al.), and total zinc concentration (Lohan et al.) were reported.
Deep-Sea Research II 49 (2002) 5365–5375
Shelf-vs. dissolution-generated alkalinity above the chemical
lysocline
Chen-Tung Arthur Chen*
Institute of Marine Geology and Chemistry, National Sun Yat-Sen University, Kaohsiung 804, Taiwan, ROC Received 15 October 2000; accepted 27 November 2001
Abstract
Processes that increase alkalinity in the upper water column facilitate the sequestration of anthropogenic CO2.
Conventional wisdom has it that most alkalinity is generated by the dissolution of calcium carbonate and that this process chiefly occurs only at great depths in the oceans. This is because most surface waters are supersaturated with respect to both calcite and aragonite; hence, calcium carbonate does not dissolve. As a result, it is widely held that most alkalinity is released into the deep oceans and that it does not enhance the ability of the oceans to absorb anthropogenic CO2at the air–sea interface. However, such anaerobic processes as sulfate reduction in the sediments on the continental
shelves do generate alkalinity that is unrelated to the dissolution of calcium carbonate. In fact, shelf-generated alkalinity may almost be as important as that generated by dissolution in the open oceans above the chemical lysocline. Globally, the former amounts to 16–31 1012mol/yr.
r2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
The behavior of the carbonate system in sea-water has long been the subject of interest to many oceanographers from various fields because it plays an important role in all three subspheres of the earth, namely the biosphere, hydrosphere, and the lithosphere. The carbonate system also
con-trols the sequestration of anthropogenic CO2,
which plays a major role in global climate change. Despite its importance, however, fundamental questions in carbonate chemistry remain to be answered. One of these seeks to find out why the oceans are notmore alkaline. This issue is central
to understanding the chemical evolution of sea-water in terms of geological timescales because the amountof dissolved calcium supplied by rivers is not great enough to account for the amount of alkalinity that is presumably removed as calcium carbonate deposits on the seabed. Assuming a steady state, calcium is apparently removed from the oceans at twice the rate it is supplied. Naturally, this leads to the conclusion that the oceans could only have achieved their present chemical composition and maintained their steady state, if there is an additional source of Ca or a yet unexplained sink of alkalinity (Mackenzie and Garrels, 1966; Milliman, 1993; de Villiers, 1998).
In order to shed light on this, de Villiers (1998) and de Villiers and Nelson (1999) investigated hydrothermal systems and pointed out that the
*Fax: +886-7-525-5346.
E-mail address:ctchen@mail.nsysu.edu.tw (C.-T.A. Chen).
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low-temperature circulation of seawater through axial mid-ocean ridge systems is much larger than the previously recognized high-temperature com-ponent. They concluded that the combined, total hydrothermal flux for Ca is consistent with its oceanic mass balance requirements. This paper aim, in part, to investigate whether or not the excess Ca values in the North Pacific are consistent with the above assessment.
One of the oldest and most strongly held paradigms in carbonate chemistry of the oceans is the conservative nature of pelagic calcium carbonate at shallow depths. Since most surface waters are supersaturated with respect to both aragonite and calcite, significant dissolution is believed to occur only at great depths (Sverdrup
etal., 1942; Chen etal., 1988a). The depth
corresponds to a critical undersaturation with regard to CaCO3, resulting in a distinct increase
in the rate of dissolution below this depth, now referred to as the lysocline (Berger, 1968; Morse, 1974). Only a few measurements of dissolution related to the lysocline have been conducted at sea. These have indicated that the aragonite and calcite lysoclines are around 800 and 3500 m, respectively, in the North Pacific (Peterson, 1966; Berger, 1967; Milliman, 1977; Troy etal., 1997).
Recently, however, Milliman et al. (1999) reported that a considerable amount of ‘‘excess’’
dissolved calcium, perhaps as much as
6080 mmol/kg, exists in the upper 5001000 m of the ocean, well above the chemical lysocline. They compared their excess calcium data with calcite dissolution rates and claimed that ... an obvious relationship is observed, providing addi-tional evidence for in situ dissolution. They further suggested that the same biological processes that prompt the rapid settling of carbonate particles (i.e. ingestion, digestion and egestion by zooplank-ton) as well as biologically mediated processes within flocculates and aggregates may be respon-sible, directly or indirectly, for much of this dissolution and the release of calcium and alkalinity. It should be pointed out that the excess Ca mentioned by Milliman et al. is not only well above the chemical lysocline, but also above the axial mid-ocean ridge systems, which implies that it is unrelated to the hydrothermal fluxes. It is
shown here that although the processes mentioned
by Milliman etal. and other researchers (e.g.
Wollastand Chou, 1998) may well take place,
those researchers may have overestimated the
CaCO3 dissolution above the lysocline. The
dis-solution of calcium carbonate may actually be even less than 30 mmol/kg in the upper 1000 m near Station ALOHA in the North Pacific Ocean where Milliman et al. presented their excess Ca values. In fact, there is hardly any dissolution (o10 mmol/kg) above the saturation depth for aragonite which is about500 m deep atthis location.
Since organic carbon decomposes mainly in the upper water column and releases CO2, the capacity
of the surface oceans to sequester anthropogenic CO2is reduced. On the other hand, processes that
increase alkalinity in the upper water column facilitate the oceanic removal of atmospheric CO2.
It is shown here that the continental shelves are clearly generating alkalinity. In fact, shelf-gener-ated alkalinity may be as important as the dissolution-generated alkalinity, thus enhancing
the removal of CO2from the atmosphere.
2. Aragonite saturation horizons
It is well known that the deep waters of the North Pacific Ocean are the oldest among all world oceans. Hence, their concentrations of carbonate ion show the lowest values of all ocean waters. The end result of low CO32concentrations
is a lower degree of saturation as well as shallower calcite and aragonite saturation horizons. Chen etal. (1988a) presented three-dimensional repre-sentations of the 100% saturation horizons for calcite and aragonite in the Pacific Ocean. Since the subject of this study focuses on the dissolution of calcium carbonate in the upper water column, only the saturation horizons for the more soluble aragonite is given (Fig. 1).
Fig. 1 also displays the depth of the 26:7st
surface, which bears a close resemblance to the 100% aragonite saturation horizon. This confor-mity indicates that circulation in the upper water column is the major factor controlling the satura-tion depths. The figure shows that the 100% saturation horizon is the shallowest in the
C.-T.A. Chen / Deep-Sea Research II 49 (2002) 5365–5375 5366
cold-water region. The depth of the aragonite saturation horizon varies from less than 200 m in the north, to 700 m at 301N and to 400 m at 151N along 1501W for which calcium data, though unpublished, are available (Chen etal., 1988b). Byrne et al. (1984) studied the dissolution rate of aragonite particulates collected with free-drifting sediment traps aboard the Discoverer cruise (Betzer et al., 1984). Their findings revealed that the depth at which a high dissolution rate of aragonite was found is shallower at high latitudes
than at mid-latitudes. These findings support the saturation horizons in Fig. 1, which shows a concave trend at mid-latitudes.
3. Dissolution of CaCO3
Milliman et al. previous dissolution estimates were primarily based on the difference between estimated carbonate exports from the euphotic zone and the mass fluxes in the sediment traps at 1000 m (Milliman 1977, 1993; Milliman and Droxler, 1996). In other words, this is from the perspective of calcium (Milliman, private commu-nication, 2000). Since there have been few studies
on the dissolution of CaCO3in the water column
based on analysis of calcium, mostof the
published results have been inferred from alkali-nity data. Alkalialkali-nity, however, also varies in accordance with the production and decomposi-tion of organic matter, nitrificadecomposi-tion and denitrifi-cation as well as sulfate reduction, etc. (Brewer and Goldman, 1976; Stumm and Morgan, 1981; Chen et al., 1982). As a result, it may be of value to use calcium data, which have a precision of about 73 mmol/kg (Olson and Chen, 1982).
Fig. 2 shows the cross-section of normalized calcium (NCa; NCa=Ca 35/S; where Ca is the
Fig. 1. One hundred percent saturation horizon of aragonite (Oa) and the st¼ 26:7 horizon in the central North Pacific.
Fig. 2. Cross-section of normalized calcium (NCa) across 1501W in the North Pacific. Values given are NCa—10,000. C.-T.A. Chen / Deep-Sea Research II 49 (2002) 5365–5375 5367
measured calcium concentration and S is salinity) along 1501W in the North Pacific. The purpose of normalization was to exclude any change caused by the removal or input of water through evaporation or precipitation. The waters below 2000 m have a 90 mmol/kg higher NCa value than the value at surface. Milliman et al. (1999) calculated the excess calcium (defined as measured dissolved calcium minus calcium calculated from a conservative relationship with salinity; Fig. 3) at
Station ALOHA (221450N, 1581W) which is
between stations 16 and 19 of the cross-section shown in Fig. 2. The vertical distribution of their excess calcium values is in reasonable agreement with the data in Fig. 2.
Shown in Fig. 3 are the aragonite saturation horizon, the aragonite chemical lysocline, the calcite dissolution rate and the calcite chemical lysocline. Although the dissolution rates are not shown, the large increase in excess calcium concentration above the aragonite chemical lyso-cline has been taken as evidence to support the hypothesis that calcium carbonate dissolves biolo-gically above this depth (Milliman et al., 1999). However, this apparent increase of Ca in subsur-face waters is not all due to calcium carbonate dissolution. Deep waters in the Pacific Ocean all originate from polar and subpolar regions in the Southern Hemisphere, which have higher calcium concentrations (Tsunogai et al., 1973; Chen et al., 1982). Fig. 4 shows the NCa for surface waters in the Pacific plotted against temperature. It is clear
Fig. 3. Excess calcium given by Milliman etal. (1999) throughout the water column at Station ALOHA, and by this study at two nearby stations. The calcite dissolution rate determined by Troy et al. (1997) is shown with the ALOHA profile based on an in situ experiment at 8 depths. Chemical lysoclines are defined as depths where the saturation state is equal to 0.8 with respect to the carbonate mineral under study. (modified from Milliman etal., 1999).
Fig. 4. Normalized surface calcium concentration vs. tempera-ture in the Pacific Ocean (closed circles; data modified from Tsunogai et al., 1973) and the Weddell Sea (crosses; data taken from Chen, 1983).
C.-T.A. Chen / Deep-Sea Research II 49 (2002) 5365–5375 5368
that the preformed NCa for cold waters is much higher than that for warm waters. The Ca data in the Weddell Sea (Chen, 1983) have been used to modify the larger data set of Tsunogai et al (1973) by assuming that circumpolar waters have the same Ca value as those in the Weddell Sea. These combined data in the Pacific give a preformed NCa equation as follows (Chen et al., 1988b): NCa1ðmmol=kgÞ ¼ 10; 240 3:53
yð76; yp201CÞ
¼ 10; 170ð75; y > 201CÞ; ð1Þ where y is the potential temperature.
This equation has been used to calculate the excess NCa (measured NCa minus the preformed NCa obtained from Eq. (1). The results and the depth at which aragonite is at 100% saturation are plotted in Fig. 5. It is now apparent that the increase in excess NCa is only 10 mmol/kg above the aragonite saturation horizon, a difference not much larger than the precision of the measure-ments. Further, the excess Ca contours also show a concave structure at mid-latitudes. The excess NCa values at two stations near Station ALOHA are also plotted in Fig. 3. The large excess Ca reported by Milliman et al. (1999) above the
aragonite chemical lysocline, without considera-tion of the preformed values, is now drastically reduced by a factor of three. It should be mentioned that the large calcium standing stock at depth may not necessarily equate to actual rates
of CaCO3dissolution (Milliman, private
commu-nication, 2000). As noted earlier, for instance, part of the increase in Ca below the lysocline is due to hydrothermal inputs (de Villiers, 1998; de Villiers and Nelson, 1999). de Villiers obtained excess Ca at a station in the North Pacific, two stations in the South Pacific and one station in the equatorial Atlantic Ocean. Her value at the shallowest sampling depth, only 4 mmol/kg, at500 m atthe station in the North Pacific (451N 1791E) is in perfect agreement with my results shown in Fig. 5. The value at the next depth, reaching 28 mmol/kg at1000 m and maximizing at54 mmol/kg at 2000 m, are also in perfectagreementwith Fig. 5. de Villier’s excess Ca values in the South Pacific and the equatorial Atlantic also do not reach 10 mmol/kg until below 1100 m, confirming that little CaCO3dissolution occurs in the upper water
column. More specifically, she estimated that Ca of hydrothermal origin is 223 mmol/kg, or 1050% of the observed Ca increase in the deep oceans. As a result, the now recalculated and much
Fig. 5. Cross-section of excess calcium across 1501W in the North Pacific. The dashed line shows where the aragonite is at 100% saturation.
reduced excess Ca has to be reduced further in order to arrive at the correct CaCO3 dissolution
rate. As Milliman has pointed out in the private communication, the excess Ca shown in Fig. 3 may
not equate to the CaCO3 dissolution rate. But,
everything else being equal, smaller excess Ca suggests smaller dissolution rates if the same age is applied.
4. Shelf-generated alkalinity
It has been shown that the excess NCa above the aragonite chemical lysocline is small. The excess NCa below the lysocline is also only 40– 50 dmol=kg; or less than half of the value reported by Milliman etal. (1999). Although Milliman etal. did not use the excess Ca data to calculate the dissolution rates, the small increase in excess NCa implies that the dissolution rate of calcium carbonate in the water column may be smaller than previously thought. Milliman et al. (1999) gave a global annual alkalinity increase of
34 1012mol/yr from CaCO3 dissolution in the
water column, 13 1012mol/yr from seafloor
dissolution and 3 1012mol/yr from
hydro-thermal vents. With 10 1012mol/yr of alkalinity added from the continental margins the global
oceans receive 60 1012mol/yr of alkalinity,
which is almost in balance with the global
carbonate production rate of 58 1012mol/yr.
Any reduction of the CaCO3 dissolution
rate would call for an additional source
of alkalinity in order to balance carbonate production. The continental margins are the most logical source.
It is interesting to examine the surface calcium concentrations and their relation to alkalinity in more detail. Fig. 4 and Eq. (1) suggest that Ca is consumed when the circumpolar surface water flows northward and increases in temperature. The decrease in Ca in the surface water (Fig. 4) is no doubt due to biological productivity which con-sumes surface water total alkalinity (TA1) and
nitrate (NO31) as well. The amountof Ca
consumed (DNCa1) is related to the consumed total alkalinity (DNTA1, where NTA1=TA1 35/
S) and nitrate (DNNO31, where NNO31=
NO31 35/S) according to the following equations
(Chen etal., 1986; Chen, 1990):
DNCa1 ¼ 0:5DNTA1 þ 0:53DNNO31; ð2Þ
NTA1 ¼ 2384 4:2yð79Þ; ð3Þ
NNO31 ¼ 25ð71:5; yp41CÞ
¼ 34 2:08yð72; 41Coyo161CÞ
¼ 0ð72; yX161CÞ: ð4Þ
Combining Eqs. (1), (2) and (4) gives a slope in the NTA1 temperature dependence of approxi-mately 8.1 which is almost twice the gradient given by Eq. (2). In other words, the measured NTA1 is much higher than those values calculated from the consumption of Ca and nitrate. Simply put, instead of an alkalinity sink, there is a large alkalinity source which is unrelated to CaCO3in
the surface waters in the Pacific Ocean. It is argued that the source may lie in the continental margins.
Indeed, itis clearly shown in Fig. 6 thatshelf
waters, especially those on the inner shelves, have an NTA value much higher than that in waters offshore. These results are based on data collected in the Bering, Yellow and East China Seas, as well as in the southern Taiwan Strait and off Sabah and Sawarak. Other data, although not shown, in-dicate similar trends (e.g., Park et al., 1969; Hattori, 1977, 1979).
The previous estimates in the literature of
10 1012mol/yr of alkalinity export from the
margins have taken into account fluvial input, neritic deposition, and the dissolution of margin-derived carbonate exports (Milliman and Droxler,
1996). Independentof calcium carbonate,
how-ever, several processes on the continental margins produce alkalinity as well whenever acids are consumed (Brewer and Goldman, 1976; Murray
etal., 1978; Stumm and Morgan, 1981; Kasten
and Jrgensen, 2000). For instance, the production of organic matter increases alkalinity by 17 mol in the generation of 106 mol of organic carbon (Redfield etal., 1963; Chen, 1978; Chen etal., 1982):
106CO2þ 122H2O þ 16HNO3
þ H3PO4-ðCH2OÞ106ðNH3Þ16H3PO4þ 138O2:
ð5Þ
C.-T.A. Chen / Deep-Sea Research II 49 (2002) 5365–5375 5370
Fig. 6. NTA vs. S diagram across shelves to a depth of 200 m for (a) the Bering Sea in winter (data taken from Chen, 1993); (b) the Yellow Sea in spring (data taken from Wang et al., 2000); (c) the East China Sea in summer (data taken from Wang and Chen, 1996); KSW denotes Kuroshio surface water; (d) the East China Sea in winter (data taken from Chen et al., 1990); (e) the southern Taiwan Strait (Wang and Chen, unpublished data) and; (f) off Sarawak, Sabah and Brunei Darussalam in the premonsoon season and (g) postmonsoon season (data taken from Snidvongs, 1999). Different symbols represent data from different cross-sections.
In the anaerobic environment on the shelves an active denitrification process can be represented by the following equation, which increases alkalinity by 83.8 mol:
ðCH2OÞ106ðNH3Þ16H3PO4þ 84:8HNO3-106CO2
þ 42:4N2þ 148:4H2O þ 16NH3þ H3PO4: ð6Þ
In addition, each NH3 released from the above
reaction can be oxidized, thereby increasing alkalinity by 0.6 mol:
5NH3þ 3HNO3-4N2þ 9H2O: ð7Þ
After the entire nitrate has been exhausted, the manganese, iron and sulfate reductions as well as methanogenesis occur ðCH2OÞ106ðNH3Þ16ðH3PO4Þ þ 236MnO2 þ 472Hþ-106CO2þ 366H2O þ 236Mnþ2þ 8N2þ H3PO4; ð8Þ ðCH2OÞ106ðNH3Þ16ðH3PO4Þ þ 424FeOOH þ 848Hþ-106CO2þ 742H2O þ 424Feþ2þ 16NH3þ H3PO4; ð9Þ ðCH2OÞ106ðNH3Þ16ðH3PO4Þ þ 53SO24 þ 106Hþ-106CO2 þ 106H2O þ 53H2S þ 16NH3þ H3PO4; ð10Þ ðCH2OÞ106ðNH3Þ16ðH3PO4Þ-53CO2 þ 53CH4þ 116NH3þ H3PO4 ð11Þ and CH4þ SO24 -HCO 3 þ HS þ H 2O: ð12Þ
Eqs. (8)–(10) increase alkalinity by 471, 847 and 105 mol, respectively, in the decomposition of 106 mol of organic carbon in each process.
Eq. (11) does notchange alkalinity
exceptmini-mally due to H3PO4. However, when the NH3
produced is oxidized to N2(Eq. (7)), the alkalinity
increases as well. Further, CH4released according
to Eq. (8) may be combined with sulfate to increase alkalinity by 2 mol for each mole of CH4
consumed. Note that each H3PO4 produced
reduces alkalinity by one (Chen et al., 1982). Recently, Chen et al. (2002) have concluded that new production amounts to only 15% of primary production averaged over the global shelves
(Knauer, 1993; Biscaye etal., 1994; Wollast,
1998; Ver etal., 1999). Thus, mostof the organic carbon produced is recycled on the shelf. As long as the recycling by means of aerobic oxidation, the reduction in alkalinity is balanced by the gain when the organic matter is produced in the first place, resulting in zero change in alkalinity. Much
Table 1
Sulfate reduction rate in different continental margin depositional environments
Location Sulfate reduction rate mmol/m2/d Reference
Limfjord (Denmark) 19 Jrgensen (1977)
Inner shelf 5 Jrgensen (1983)
Outer shelf 0.560.84 Jrgensen (1983)
Gulf of St. Lawrence 0.755 Edenborn etal. (1987)
Gulf of Maine 0.362.7 Christensen (1989)
Washington shelf 14 Christensen (1989)
E. Australian slope 0.0070.56 Heggie etal. (1990)
Gulf of Mexico shelf 2.113.8 Lin and Morse (1991)
Gulf of Mexico slope 0.0387.66 Lin and Morse (1991)
Skagerrak 0.844 Canfield etal. (1993)
Washington State slope 0.651.3 Devol and Christensen (1993)
ECS shelf 0.93 Huang and Lin (1995)
Chilean slope 2.4 Fossing etal. (1995)
Peruvian slope 5.225.5 Fossing etal. (1995)
Chilean shelf 0.560.79 Thamdrup and Canfield (1996)
Svalbard shelf 1.78.4 Sagemann etal. (1998)
Gotland basin (Baltic Sea) 0.83.68 Greeff etal. (1998)
SE Atl. cont. margin 0.0914 Ferdelman etal. (1999)
C.-T.A. Chen / Deep-Sea Research II 49 (2002) 5365–5375 5372
of the new production, however, leaves the water column, thereby increasing alkalinity according to Eq. (2). Next, the denitrification and reduction of organic matter by manganese, iron, sulfate as well as methanozenesis all increase alkalinity.
Chen and Wang (1999) estimated that the East China Sea generates between 1.0770.8 and 1.871.8 mol/m2
/yr of alkalinity with over 80% contributed by iron and sulfate reductions. These rates vary by about two orders of magnitude worldwide, but the sulfate reduction rate for the ECS shelf is consistent with other continental margin regions (Table 1). Nevertheless, Huang and Lin (1995) reported that the iron and sulfate reduction rates in the ECS are higher than in other places may be by 30–50%; hence, the average global rate for shelf-generated alkalinity is perhaps
between 0.6 and 1.2 mol/m2/yr. By taking the
global shelf area as 26 106km2 (Wollast, 1998),
these rates correspond to between 16 and
31 1012mol/yr of global shelf-generated alkali-nity, which is independent of the dissolution of
CaCO3. Although the horizontal extent of these
shelf-generated alkalinity signal is not known, this amountcannotbe ignored when compared with the global oceanic alkalinity production rate of
50–72 1012mol/yr estimated by Broecker and
Peng (1982), Morse and Mackenzie (1990), Wol-last(1994), Archer (1996) and Milliman and Droxler (1996).
5. Conclusions
The increase in normalized Ca below 500 m after being corrected for the difference in preformed NCa is in perfect agreement with the results of de Villiers (1998) in the North Pacific Ocean. How-ever, the increase above the lysocline is only 10 mmol/kg, suggesting low dissolution rates above the chemical lysocline in the North Pacific. As a result, the rate of release of alkalinity is also low. On the other hand, denitrification, as well as manganese, iron and sulfate reductions on the continental shelves all generate alkalinity which
occurs regardless of the dissolution of CaCO3.
Despite obvious uncertainties, the global shelf-generated alkalinity is estimated at between 16 and
31 1012mol/yr, which is of the same order as that generated by the open ocean dissolution of CaCO3.
Acknowledgements
This work was supported by the National Science Council of the Republic of China (NSC 90-2611-M-110-004). J.D. Milliman, L. Miller, R.H. Byrne and an anonymous reviewer provided valuable comments which have helped to improve the manuscript.
References
Archer, D.E., 1996. A data-driven model of the global calcite lysocline. Global Biogeochemical Cycles 10, 511–526. Berger, W.H., 1967. Foraminifera ooze: solution at depth.
Science 156, 383–385.
Berger, W.H., 1968. Planktonic foraminifera: selective solution and paleoclimatic interpretation. Deep-Sea Research 15, 31–43.
Betzer, P.R., Byrne, R.M., Acker, J.G., Lewis, G.S., Jolley, R.R., Feely, R.A., 1984. The oceanic carbonate system: a reassessmentof biogenic controls. Science 226, 1074–1077. Biscaye, P.E., Flagg, C.N., Falkowski, P.G., 1994. The shelf
edge exchange processes experiment, SEEP-II: an introduc-tion to hypotheses, results and conclusions. Deep-Sea Research II 41, 231–252.
Brewer, P.G., Goldman, J.C., 1976. Alkalinity changes generated by phytoplankton growth. Limnology and Oceanography 21, 108–117.
Broecker, W.S., Peng, T.H., 1982. Tracers in the Sea. Lamont-Doherty Geology Observatory, Palisades, New York, pp. 690.
Byrne, R.H., Acker, J.G., Betzer, P.R., Feely, R.A., Cates, M.H., 1984. Water column dissolution of aragonite in the Pacific Ocean. Nature 312, 321–326.
Canfield, D.E., Thamdrup, B., Hansen, J.W., 1993. The anaerobic degradation of organic matter in Danish coastal sediments: iron reduction, manganese reduction, and sulfate reduction. Geochimica et Cosmochimica Acta 57, 3867–3883.
Chen, C.T., 1978. Decomposition of calcium carbonate and organic carbon in the deep oceans. Science 201, 735–736. Chen, C.T., 1983. Distributions of dissolved calcium and
alkalinity in the Weddell Sea in winter. US Antarctic Journal, p. 136–137.
Chen, C.T.A., 1990. Decomposition rate of calcium carbonate and organic carbon in the North Pacific Ocean. Journal of the Oceanography Society of Japan 46, 201–210.
Chen, C.T.A., 1993. Carbonate chemistry of the wintertime Bering Sea marginal ice zone. Continental Shelf Research 13, 67–87.
Chen, C.T.A., Wang, S.L., 1999. Carbon, alkalinity and nutrient budget on the East China Sea Continental Shelf. Journal of Geophysical Research 104, 20675–20686. Chen, C.T., Pytkowicz, R.M., Olson, E.J., 1982. Evaluation of
the calcium problem in the South Pacific. Geochemical Journal 16, 1–10.
Chen, C.T.A., Rodman, M.R., Wei, C.L., Olson, E.J., Feely, R.A., Gendron, J.F., 1986. Carbonate Chemistry of the North Pacific Ocean. US Department of Energy Technical Report, DOE/NBB-0079, p. 176.
Chen, C.T.A., Feely, R.A., Gendron, J.F., 1988a. Lysocline, calcium carbonate compensation depth, and calcareous sediments in the North Pacific. Pacific Science 42, 237–252.
Chen, C.T.A., Rodman, M.R., Wei, C.L., Olson, E.J., Feely, R.A., Gendron, J.F., 1988b. CDIAC numeric data collec-tion, Carbonate Chemistry of the North Pacific Ocean, Oak Ridge National Laboratory Report NDP-029, p. 201. Chen, C.T.A., Luo, L., Chen, J.W., Huang, M.S., Lin, J.S.,
Chang, C., Chen, J.C., 1990. Preliminary Reportof Ocean Researcher 1 Cruise 191: December 18–20, 1988, off Northeastern Taiwan. Institute of Marine Geology, National Sun Yat-Sen University Technical Report 9, p. 75 (in Chinese).
Chen, C.T.A., Liu, K.K., MacDonald, R., 2002. Continental margin exchanges. In: Fasham, M.J.R. (Ed.), Ocean Biogeochemistry: a JGOFS Synthesis (revised). Springer, Berlin.
Christensen, J.P., 1989. Sulfate reduction and carbon oxidation rates in continental shelf sediments, an examination of offshelf carbon transport. Continental Shelf Research 9, 223–246.
de Villiers, S., 1998. Excess dissolved Ca in the deep ocean: a hydrothermal hypothesis. Earth and Planetary Science Letters 164, 627–641.
de Villiers, S., Nelson, B.K., 1999. Dectection of low-temperature hydrothermal fluxes by seawater Mg and Ca anomalies. Science 285, 721–723.
Devol, A.H., Christensen, J.P., 1993. Benthic fluxes and nitrogen cycling in sediments of the continental margin of the eastern North Pacific. Journal of Marine Research 51, 345–372.
Edenborn, H.M., Silverberg, N., Mucci, A., Sundby, B., 1987. Sulfate reduction in coastal marine sediments. Marine Chemistry 21, 329–345.
Ferdelman, T.G., Fossing, H., Neumann, K., Schulz, H.D., 1999. Sulfate reduction in surface sediments of the southeast Atlantic continental margin between 151380S and 271570S
(Angola and Namibia). Limnology and Oceanography 44, 650–661.
Fossing, H., Gallardo, V.A., Jrgensen, B.B., H.uttel, M., Nielsen, L.P., Schulz, H., Canfield, D.E., Foster, S., Glud, R.N., Gundersen, J.K., K.uver, J., Ramsing, N.B., Teske, A., Thamdrup, B., Ulloa, O., 1995. Concentration and
transport of nitrate by the mat-forming sulphur bacterium Thioploca. Nature 374, 713–715.
Greeff, O., Glud, R.N., Gundersen, J., Holby, O., Jorgensen, B.B., 1998. A benthic lander for tracer studies in the sea bed: in situ measurements of sulfate reduction. Continental Shelf Research 18, 1581–1594.
Hattori, A., 1977. Preliminary Report of the Hakuho Maru Cruise KH-75-4. Ocean Research Institute, University of Tokyo, p. 87.
Hattori, A., 1979. Preliminary Report of the Hakuho Maru Cruise KH-78-3. Ocean Research Institute, University of Tokyo, p. 87.
Heggie, D.T., etal., 1990. Organic carbon cycling and modern phosphorite formation on the East Australian continental margin: an overview. In: Notholt, A.J.G., Javis, I. (Eds.), Phosphorite Research and Development. Special Publish 52, Geology Society London, pp. 87–118.
Huang, K.M., Lin, S.W., 1995. The carbon-sulfide-iron relationship and sulfate reduction rate in the East China Sea continental shelf sediments. Geochemical Journal 29, 301–315.
Jrgensen, B.B., 1977. The sulfur cycle of a coastal marine sediment(Limfjorden, Denmark). Limnology and Oceano-graphy 22, 814–832.
Jrgensen, B.B., 1983. Processes at the sediment–water inter-face. In: Bolin, B., Cook, R.C. (Eds.), The Major Biogeochemical Cycles and their Interactions. SCOPE, pp. 477–509.
Kasten, S., Jrgensen, B.B., 2000. Sulfate reduction in marine sediments. In: Schulz, H.D., Zabel, M. (Eds.), Marine Geochemistry. Springer, Berlin, pp. 263–281.
Knauer, G.A., 1993. Productivity and new production of the oceanic system. In: Wollast, R., Mackenzie, F.T., Chou, L. (Eds.), Interactions of C, N, P and S Biogeochemical Cycles and Global Change. Springer, Berlin, pp. 211–231. Lin, S., Morse, J.W., 1991. Sulfate reduction and iron sulfide
mineral formation in Gulf of Mexico anoxic sediments. American Journal of Science 291, 55–59.
Mackenzie, F.T., Garrels, R.M., 1966. Chemical mass balance between rivers and oceans. American Journal of Science 264, 507–525.
Milliman, J.D., 1977. Dissolution of calcium carbonate in the Sargasso Sea (northwest Atlantic). In: Anderson, N., Malahof, A. (Eds.), Fate of Fossil Fuel CO2in the Oceans.
Plenum Press, New York, pp. 641–653.
Milliman, J.D., 1993. Production and accumulation of calcium carbonate in the ocean: budget. Global Biogeochemical Cycles 7, 927–957.
Milliman, J.D., Droxler, A.W., 1996. Neritic and pelagic carbonate sedimentation in the marine environment: Ignor-ance is notbliss. Geologische Rundschau 85, 496–504. Milliman, J.D., Troy, P.J., Balch, W.M., Adams, A.K., Li,
Y.H., Mackenzie, F.T., 1999. Biologically mediated dis-solution of calcium carbonate above the chemical lysocline? Deep-Sea Research I 46, 1653–1669.
Morse, J.W., 1974. Dissolution kinetics of calcium carbonate in seawater. V. Effects of natural inhibitors and the position of C.-T.A. Chen / Deep-Sea Research II 49 (2002) 5365–5375
the chemical lysocline. American Journal of Science 274, 638–647.
Morse, J.W., Mackenzie, F.T., 1990. Geochemistry of Sedi-mentary Carbonates. Elsevier, New York, 707pp. Murray, J.W., Grundmanis, V., Smethie Jr., W.M., 1978.
Interstitial water chemistry in sediments of Saanich inlet. Geochimica etCosmochimica Acta 42, 1011–1026. Olson, E.J., Chen, C.T., 1982. Interference in the determination
of calcium in seawater. Limnology and Oceanography 27, 375–380.
Park, P.K., Webstr, G.R., Yamamoto, R., 1969. Alkalinity budgetof the Columbia River. Limnology and Oceano-graphy 14, 559–567.
Peterson, M.N.A., 1966. Calcite: rates of dissolution in a vertical profile in the central pacific. Science 154, 1542–1544. Redfield, A.C., Ketchum, B.H., Richards, F.A., 1963. The influence of organisms on the composition of seawater. In: Hill, M.N. (Ed.), The Sea, Vol. 2. Wiley-Interscience, New York, pp. 26–77.
Sagemann, J., Jrgensen, B.B., Greeff, O., 1998. Temperature dependence and rates of sulfate reduction in cold sediments of Svalbard, Arctic Ocean. Geomicrobiological Journal 15, 85–100.
Snidvongs, A., 1999. Dissolved carbonate-carbon dioxide in sea water of the South China Sea. Area II: Sarawak, Sabah and Brunei Darussalam waters. In: Proceedings of the Second Technical Seminar on Marine Fishery Resources Survey in the South China Sea, Area II, West Coast of Sabah, Sarawak and Brunei Darussalam, 14–15 December 1998, Kuala Lumpur, Malaysia, pp. 62–94.
Stumm, W., Morgan, J.J., 1981. Aquatic Chemistry, 2nd edition. Wiley, New York.
Sverdrup, H.U., Johnson, M.W., Fleming, R.H., 1942. The Oceans. Prentice-Hall, Englewood Cliffs, NJ, p. 1087. Thamdrup, B., Canfield, D.E., 1996. Pathways of carbon
oxidation in continental margin sediments off central Chile. Limnology and Oceanography 41, 1629–1650.
Troy, P.J., Li, Y.H., Mackenzie, F.T., 1997. Changes in surface morphology of calcite exposed to the oceanic water column. Aquatic Geochemistry 3, 1–20.
Tsunogai, S., Yamahata, H., Kudo, S., Saito, O., 1973. Calcium in the Pacific Ocean. Deep-Sea Research 20, 717–726. Ver, L.M.B., Mackenzie, F.T., Lerman, A., 1999.
Biogeochem-ical responses of the carbon cycle to natural and human perturbations: past, present, and future. American Journal of Science 299, 762–801.
Wang, S.L., Chen, C.T.A., 1996. Comparison of seawater carbonate parameters in the East China Sea and the Sea of Japan. La mer 34, 131–136.
Wang, S.L., Chen, C.T.A., Hong, G.H., Chung, C.S., 2000. Carbon dioxide and related parameters in the East China Sea. Continental Shelf Research 20, 525–544.
Wollast, R., 1994. The relative importance of biomineralization and dissolution of CaCO3 in the global carbon cycle.
Bulletin of the Institute of Oceanography. Monaco, Special no. 13, pp. 13–35.
Wollast, R., 1998. Evaluation and comparison of the global carbon cycle in the coastal zone and in the open ocean. In: Brink, K.H., Robinson, A.R. (Eds.), The Sea, Vol. 10. Wiley, New York, pp. 213–252 (Chapter 9).
Wollast, R., Chou, L., 1998. Distribution and fluxes of calcium carbonate along the continental margin in the Gulf of Biscay. Aquatic Geochemistry 4, 369–393.
Continental Shelf Research 23 (2003) 387–391
Research note
Rare northward flow in the Taiwan Strait in winter: a note
Chen-Tung Arthur Chen*
Institute of Marine Geology and Chemistry, National Sun Yat-Sen University, P.O. Box 59-60, Kaohsiung 80424, Taiwan, ROC Received 21 March 2002; received in revised form 26 September 2002; accepted 15 November 2002
Abstract
Conventional wisdom is that, in winter, the China Coastal Current flows southward on the western part of the Taiwan Strait, but on the eastern part of the Strait, a branch of the Kuroshio flows northward. The net flux is subject to debate, but it is believed to be small. This author opted to choose a northward flux of 0.2 Sv. Others believe that there is zero net flux, or the net flow may even be towards the south. Thus, it is very surprising to find a net northward flux as much as 2.74 Sv in early March 1997 (reported).
Historical data are presented here to show that the salinity, temperature and nutrient concentrations are relatively homogeneous in the Taiwan Strait, in summer. The high salinity and temperature, but low nutrients, suggest that the water originates from the South China Sea (SCS) or the Kuroshio. In winter, on the other hand, steady and strong NE winds push the fresh, cold, nutrient-rich China coastal water southward, along the western part of the Taiwan Strait. Some salty and warm, but still nutrient-poor, SCS or Kuroshio water flows northward on the eastern part of the Strait. The present author concludes that the observed northward flux in early 1997 was caused by a sudden relaxation of the steady NE wind. As a result, any seawater that would have moved northward, but had been halted for several months by the NE wind, moved suddenly northward. Indeed, rarely occurring southerly wind in winter was observed briefly during the research cruise. Other physicochemical parameters of the waters suggest also that the observed northward-flowing water had originated mainly from the southward-flowing China Coastal Current, rather than the SCS or the Kuroshio. The physicochemical data support also the concept that the western part of Taiwan Strait was occupied by the China Coastal Current, which normally flows southward in winter.
r2003 Elsevier Science Ltd. All rights reserved.
Keywords: Taiwan Strait; East China Sea; South China Sea; Nutrients; Flux; Winter monsoons
1. Introduction
It has been known for many years that the Kuroshio contributes nutrients to the East China Sea (ECS) (Wong et al., 1991; Liuet al., 1992;
Chen et al., 1995;Gong et al., 1995). Indeed,Chen
(1996)identified upwelling of the Kuroshio Inter-mediate Water (KIW) as the major source of nutrients, to sustain the high productivity on the
ECS shelf.Chen and Wang (1999)concluded that
the upwelled sub-surface Kuroshio water supplied 71% of phosphorus (P) to the ECS shelf, with the remaining 15% derived from the Taiwan Strait, 6% from rivers and groundwater combined, 5% from dust, and 3% from the Kuroshio surface waters. The upwelled sub-surface Kuroshio water
*Corresponding author. Tel.: 7-525-5146; fax: +886-7-525-5346.
E-mail address:ctchen@mail.nsysu.edu.tw (C.-T.A. Chen).
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supplies a smaller, but still large, percentage of nitrogen (N), 49%. The remaining N comes from
rivers and groundwater (33%), precipitation
(10%), the Taiwan Strait (8%) and Kuroshio
surface waters (o1%).
Liuet al. (2000), on the other hand, concluded that ‘‘nutrient fluxes from the Taiwan Straity changed drastically between seasons, ranging from less than half to more than double the Kuroshio inputs’’. The high nutrient fluxes were attributed mainly to high volume transport, which was found to be higher in winter. Nutrient concentrations in the Taiwan Strait waters were found also to be higher in winter, than in summer. This paper questions the conclusion of a high northward volume transport during winter.
2. Winds and flow patterns
Taiwan Strait is located in a monsoonal region with southwesterly winds in summer, but north-easterly winds in winter. Since a branch of Kuroshio tends to flow northward all the year round, in summer the flow coincides with winds that blow in the same direction. As a result, waters
across the Strait all flow northward (Chern and
Wang, 1992; Chuang, 1986), as evidenced by the relative homogeneous salinity and temperature (Fig. 1(a) and (c)). In winter, steady and strong NE winds push the fresh, cold China coastal water to flow southward. At the same time, some salty and warm Kuroshio waters manage to flow northward on the eastern part of the strait,
resulting in a small net northward flow (Wang
and Chern, 1988;Huet al., 1999c).Figs. 1(b) and
(d) show the east–west salinity and temperature
distributions in winter, which is in agreement with the above assessment. Realizing that the north-ward flux is compensated by the southnorth-ward flux,
Chen and Wang (1999) chose to use a net northward flow of 0.2 Sv in winter, whilst P. Hsueh (pers. comm., 2000) even feels that the net flow may be zero; it is why evenLiuet al. (2000), themselves, were surprised to find a fairly high northward volume transport (2.74 Sv) from the Taiwan Strait in winter. These investigators quoted also previous studies that indicated
south-ward (e.g.Fan, 1979) or partly southward (Nitani, 1972) flows.
The reason for the large discrepancy may lie in
the fact that Liuet al. (2000) made winter
observations during a brief period when the NE
winds suddenly turned towards the south. Fig. 2
shows the winds observed at PenghuIsland located in the Taiwan Strait. It is immediately clear that, for the months prior to the cruise in early March, the north north-east (NNE) winds were strong and steady. Around the time of the observations, however, the NNE winds weakened, they even switched direction, by 1801. As a result, the piled-up water rushed northward when the winds turned.Liuet al. (2000)noted that previous investigators had illustrated the possible fluctuat-ing flow directions along the southeastern shelf of China; these may have resulted from the alternat-ing intensification and relaxation of the north-eastern monsoon. The present author agrees with the suggestion ofLiuet al. (2000)that ‘‘yIn the light of the variability of the shelf environment, more observations are needed to better determine the mean condition of this transport’’.
3. Discussion
Elsewhere, Liuet al. (2000) reported higher
nutrient concentrations in the Taiwan Strait in winter. This information should have led to the conclusion that the large northward flow could not have originated from the south, as waters in the south have low nutrient concentrations. Fig. 1(e) and (g)indicate that the waters are uniformly low in nutrients in and around Taiwan Strait, in summer.Fig. 1(f) and (h)indicate that, in winter, the nutrient concentrations remain low in the southern part of the Taiwan Strait, except near the coast of China. However, within the Taiwan Strait, phosphorus and silicate concentrations more than doubled. Nitrate increased by an order of magnitude within the western part of the strait, yet the eastern portion remained low in nutrients. There is no doubt that such high nutrients originate from the Changjiang (Yangtze River) and the coastal regions of the mainland, and the
waters must have flowed southward. What Liu
C.-T.A. Chen / Continental Shelf Research 23 (2003) 387–391 388
Fig. 1. Distribution of surface salinity (a, b), temperature (c, d), nitrate (e, f), phosphate (g, h) and silicate (i, j) concentration in the vicinity of Taiwan Strait in August and February (data taken fromWang, 1991;Wong et al., 1991;Chen, 1992;Chen, 1996;Hong and Dai, 1994;Chen et al., 1995, 1996;Wang and Chen, 1998;Fujien Oceanological Institute, 1998;Chen and Wang, 1998, 1999;Huet al., 1999a,b;Gong et al., 2000;Liuet al., 2000;Wang et al., 2000; and references therein).
et al. (2000)observed were waters that had flowed southward, but only reversed their direction briefly during the observation period. Nitrate concentra-tions increase more than those of phosphate, because Chinese rivers have an N/P ratio of over 100.
It should be noted that there is a prominent N–S temperature front in the Taiwan Strait, in winter (Fig. 3). The signal is lacking totally in summer. It starts to develop in the fall and fades away in spring. Coastal upwelling or vertical mixing may result in the temperature front with lower
Fig. 3. Seasonal probability maps of temperature fronts for 1995–1996. The color bar shows the probability scale (courtesy I. Belkin;
Hickox et al., 2000).
date
1/1/97 2/1/97 3/1/97 3/31/97
wind speed , dm/sec
-100 -80 -60 -40 -20 0 20 40
NNE (av. 5.6m/sec) S(av. 3m/sec)
Fig. 2. Winds recorded at Penghuin early 1997.
C.-T.A. Chen / Continental Shelf Research 23 (2003) 387–391 390
temperature, but higher nutrients on the coastal side. However, local upwelling or vertical mixing could not have resulted in such low temperatures, but high nutrient concentrations, as shown in
Fig. 1(d), (f) and (h). This is because the bottom water is not that cold. Further, the water column nutrient inventories have increased by about the same ratio as the surface concentrations.
Acknowledgements
The paper benefited from discussions with Prof. C.T. Liuof the National Taiwan University. Prof. I. Belkin providedFig. 3, Prof. A. Isobe provided valuable comments, and the ROC National Science Council supported the research (NSC 90-2611-M-110-004).
References
Chen, C.T.A., 1996. The Kuroshio intermediate water is the major source of nutrients on the East China Sea continental shelf. Oceanologica Acta 19, 523–527.
Chen, C.T.A., Wang, S.L., 1998. Influence of intermediate water in the western Okinawa Trough by the outflow from the South China Sea. Journal of Geophysical Research 103, 12683–12688.
Chen, C.T.A., Wang, S.L., 1999. Carbon, alkalinity and nutrient budget on the east China Sea Continental Shelf. Journal of Geophysical Research 104, 20675–20686. Chen, C.T.A., Ruo, R., Pai, S.C., Liu, C.T., Wong, G.T.F.,
1995. Exchange of water masses between the East China Sea and the Kuroshio off northeastern Taiwan. Continental Shelf Research 15, 19–39.
Chen, C.T.A., Lin, C.M., Huang, B.T., Chang, L.F., 1996. The stoichiometry of carbon, hydrogen, nitrogen, sulfur and oxygen in the particular matter of the western North Pacific marginal seas. Marine Chemistry 54, 179–190.
Chen, D.X., 1992. Marine Atlas of Bohai Sea, Yellow Sea, East China Sea: Hydrology. China Ocean Press, Beijing, pp. 524 (in Chinese).
Chern, C.S., Wang, J., 1992. The influence of Taiwan Strait waters on the circulation of the South China Sea. La mer 30, 223–228.
Chuang, W.S., 1986. A note on the driving mechanisms of current in the Taiwan Strait. Journal of the Oceanography Society of Japan 42, 355–361.
Fan, K.L., 1979. On upwelling off the Peng-Hu islands. Acta Oceanographic Taiwanica 9, 50–57.
Fujien Oceanological Institute, 1998. A Comprehensive Oceano-graphic Survey of the Central and Northern Part of the Taiwan Strait. Kexue Pub. Co., Beijing, pp. 423 (in Chinese).
Gong, G.C., Liu, K.K., Pai, S.C., 1995. Prediction of nitrate concentration from two end member mixing in the southern East China Sea. Continental Shelf Research 15, 827–842. Gong, G.C., Shiah, F.K., Liu, K.K., Wen, Y.H., Liang, M.H.,
2000. Spatial and temporal variation of chlorophyll a, primary productivity and chemical hydrography in the southern East China Sea. Continental Shelf Research 20, 411–436. Hickox, R., Belkin, I., Cornillon, P., Shan, Z.Q., 2000.
Climatology and seasonal variability of ocean fronts in the East China, Yellow and Bohai Seas from satellite SST data. Geophysical Research Letters 27, 2945–2948.
Hong, H.S., Dai, M.H., 1994. Biogeochemical studies of biologically important elements in the Taiwan Strait. In: Di Zhou, et al. (Eds.), Oceanology of China Seas, Vol. V1, pp. 201–212.
Hu, J.Y., Liang, H.X., Zhang, X.B., 1999a. Sectional distribution of salinity and its indication of Kuroshio’s intrusion in the southern Taiwan Strait and northeastern South China Sea late summer, 1994. Acta Oceanologica Sinica 18, 225–236. Hu, J.Y., Liang, H.X., Zhang, X.B., 1999b. Distributional
features of temperature and salinity in the southern Taiwan Strait and its adjacent sea areas in late summer, 1994. Acta Oceanologica Sinica 18, 237–246.
Hu, J.Y., Hong, H.S., Chen, Z.Z., He, Z.G., Hong, J.S., Liang, H.X., 1999c. Analysis on features of temperature and salinity in the northern Taiwan Straits during February– March, 1998. Marine Science Bulletin 18, 11–16 (in Chinese with English abstract).
Liu, K.K., Gong, G.C., Lin, S., Wang, C.Y., Wei, C.L., Pai, S.C., Wu, C.K., 1992. The year-round upwelling at the shelf break near the northern tip of Taiwan as evidenced by chemical hydrography. Terrestrial, Atmospheric and Ocea-nic Sciences 3, 243–275.
Liu, K.K., Tang, T.Y., Gong, G.C., Chen, L.Y., Shiah, F.K., 2000. Cross-shelf and along-shelf nutrient fluxes derived from flow fields and chemical hydrography observed in the southern East China Sea off northern Taiwan. Continental Shelf Research 20, 493–523.
Nitani, H., 1972. The beginning of the Kuroshio. In: Stommel, H., Yoshida, K. (Eds.), Kuroshio. University of Tokyo Press, Tokyo, pp. 129–156.
Wang, Y.H., 1991. Marine Atlas of Boshi Sea, Yellow Sea, East China Sea, Chemistry. China Ocean Press, Beijing, pp. 257. Wang, J., Chern, C.S., 1988. On the Kuroshio branch in the Taiwan strait during wintertime. Progress in Oceanography 21, 469–491.
Wang, S.L., Chen, C.T.A., 1998. Bottom water at the center of the north East China Sea in summer: remnant winter water. Continental Shelf Research 18, 1573–1580.
Wang, S.L., Chen, C.T.A., Hong, G.H., Chung, C.S., 2000. Carbon dioxide and related parameters in the East China Sea. Continental Shelf Research 20, 525–544.
Wong, G.T.F., Pai, S.C., Liu, K.K., Chen, C.T.A., 1991. Variability of the chemical hydrography at the frontal region between the East China Sea and the Kuroshio northeast of Taiwan. Estuarine Coastal and Shelf Science 33, 105–120.
