Influence of export rain ratio changes on atmospheric CO<Subscript>2</Subscript> and sedimentary calcite preservation

The responses of atmospheric pCO₂ and sediment calcite content to changes in the export rain ratio of calcium carbonate to organic carbon are examined using a diffusion-advection ocean biogeochemical model coupled to a one-dimensional sediment geochemistry model. Our model shows that a 25% reduction in rain ratio decreases atmospheric pCO₂ by 59 ppm. This is caused by alkalinity redistribution by a weakened carbonate pump and an alkalinity increase in the whole ocean via carbonate compensation with decreasing calcite burial. The steady state responses of sedimentary calcite content and calcite preservation efficiency are rather insensitive to the deepening of the saturation horizon of 1.9 km. This insensitivity is a result of the reduced deposition flux that decreases calcite burial, counteracting the saturation horizon deepening that increases calcite burial. However, in the first 10,000 years the effect of reduced calcite deposition on the burial change is more prominent; while after 10,000 years, the effect of saturation horizon deepening is more dominant. The lowering of sediment calcite content for the first 10,000 years is effectively decoupled from the 1.9 km downward shift of the saturation horizon. Our results are in part a consequence of the more dominant role that respiration CO₂ plays in sediment calcite dissolution over bottom water chemistry in our control run and support the decoupling of calcite lysocline depth and saturation horizon shifts, as suggested originally by Archer and Maier-Reimer (1994) and Archer et al. (2000).     

A new look at the alkalinity of the Sea of Japan

The most important feature of the distribution of the alkalinity and calcium in the Sea of Japan—the increase in the potential alkalinity with depth under the conditions when the waters are supersaturated in relation to calcium carbonate—is considered. It is demonstrated that this fact cannot be accounted for by the reaction of the formation-dissolution of calcium carbonate. A new concept explaining the alkalinity distribution in the sea is proposed. According to it, the biological pump is the basic process responsible for the alkalinity transport from the euphotic layer into the interior of the sea. Photosynthesis is the driving force for this process. The role of the active element transporting the alkalinity is not calcium carbonate, as has been claimed elsewhere, but extracellular polysaccharides (EPSs) produced by phytoplankton. EPSs bind to calcium and other cations to form transparent exopolymer particles (TEPs). The proposed conception makes it possible to explain the following: (a) the vertical flux of calcium carbonate that is independent of the super-saturation—undersaturation state of the ambient water regarding calcium carbonate; (b) the existence of the calcium carbonate flux regardless of the nature of the plankton skeletons; (c) the nonstoichiometric ratio between the alkalinity and calcium fluxes.     

海洋生物泵研究进展

海洋生物泵是以一系列海洋生物为介质将大气中的碳输运到海洋深层的过程,是海洋碳循环的重要组成部分以及未来的研究重点。本文系统地描述了海洋生物泵碳汇几个主要阶段:浮游植物沉降,浮游动物粪球颗粒沉降,透明胞外聚合颗粒物(TEP)沉降和海雪沉降以及碳酸盐反向泵过程。同时,本文对南海生物泵的研究进展进行简要介绍,服务于中国海碳循环。     

A preliminary study of carbon system in the East China Sea

In the central part of the East China Sea, the activity of CO₂ in the surface water and total carbonate, pH and alkalinity in the water column were determined in winter and autumn of 1993. The activity of CO₂ in the continental shelf water was about 50 ppm lower than that of surface air. This decrease corresponds to the absorption of about 40 gC/m²/yr of atmospheric CO₂ in the coastal zone or 1 GtC/yr in the global continental shelf, if this rate is applicable to entire coastal seas. The normalized total carbonate contents were higher in the water near the coast and near the bottom. This increase toward the bottom may be due to the organic matter deposited on the bottom. This conclusion is supported by the distribution of pH. The normalized alkalinity distribution also showed higher values in the near-coast water, but in the surface water, indicating the supply of bicarbonate from river water. The residence time of the East China Sea water, including the Yellow Sea water, has been calculated to be about 0.8 yr from the excess alkalinity and the alkalinity input. Using this residence time and the excess carbonate, we can estimate that the amount of dissolved carbonate transported from the coastal zone to the oceanic basin is about 70 gC/m²/yr or 2 GtC/yr/area-of-global-continental-shelf. This also means that the rivers transport carbon to the oceans at a rate of 30 gC/m²/yr of the coastal sea or 0.8 GtC/yr/ area-of-global shelf, the carbon consisting of dissolved inorganic carbonate and terrestrial organic carbon decomposed on the continental shelf.     

Understanding the export of biogenic particles in oceanic waters: Is there consensus?

We examine progress towards a global view of oceanic export of particulate organic carbon (POC) and other nutrient elements (P, N, Si) from the surface (upper 100 m), through the subsurface, to the deep sea (>1000 m), focusing on syntheses published since 1999 and on the Joint Global Ocean Flux Study. Food-web structure is important, and surface and subsurface processes contribute similarly to determine the fraction of net primary production (NPP) reaching the deep sea. NPP by large cells generally favours high surface export of POC. Preferential remineralization of P and N (versus C) with depth is common, as is regional variation in subsurface POC flux attenuation.The role of mineral fluxes is complex. Annual mean fluxes of POC and minerals are correlated in global deep sediment trap records, but causality and the relative importance of different minerals depends on the assumptions made. Time-series observations at single sites can oppose the geographic trends, and their large seasonal variability in the contribution of POC to total flux is at odds with mechanistic models for POC transport by minerals. Despite generally positive correlations between biogenic carbonate and POC fluxes, the overall role of carbonate export is to decrease the transfer of carbon dioxide from the atmosphere to the ocean. Both autotrophs and heterotrophs produce minerals, and progress in separating these contributions is required for the deconvolution of mineral ballast and food-web effects.Many recent models suggest global surface POC export of ∼10 GTC/yr, despite widely varying biological complexity. This limits the usefulness of their prediction of ecosystem and carbon cycle responses to global change. Progress requires better observations for model validation, and more efforts to relate the models to the observed complexity, rather than to overly simplified global syntheses. We advocate more time-series stations targeting under-studied biogeochemical regions, development of automated in situ tools for study of the subsurface ocean, and increased emphasis on combining ecological and biogeochemical methods.     

Budget and Fluxes of Particulate Organic Carbon and Nitrogen According to the Data on Their Vertical Distribution in the Deep Part of the Black Sea

On the basis of the analysis of the many-year data on the vertical distributions of particulate organic carbon and nitrogen, we compute their annual average amounts for three typical layers of water in the deep part of the Black Sea: for a layer located above the oxycline and characterized by the formation of new portions of particulate organic matter in the course of photosynthesis, inside the oxycline, where the major part of oxygen is consumed and the major part of the flux of particulate organic matter is oxidized, and for the upper part of the anoxic zone characterized by the most active microbiological processes of oxidation of the organic substances and production of sulfides. The available literature data on sedimentation traps are used to study the downward annual average fluxes of particulate organic matter from the euphotic zone into the oxycline and into the anaerobic zone. The seasonal variability of the amounts and fluxes of particulate carbon and nitrogen is revealed.     

Preindustrial, historical, and fertilization simulations using a global ocean carbon model with new parameterizations of iron limitation, calcification, and N2 fixation

The Canadian Model of Ocean Carbon (CMOC) has been developed as part of a global coupled climate carbon model. In a stand-alone integration to preindustrial equilibrium, the model ecosystem and global ocean carbon cycle are in general agreement with estimates based on observations. CMOC reproduces global mean estimates and spatial distributions of various indicators of the strength of the biological pump; the spatial distribution of the air-sea exchange of CO₂ is consistent with present-day estimates. Agreement with the observed distribution of alkalinity is good, consistent with recent estimates of the mean rain ratio that are lower than historic estimates, and with calcification occurring primarily in the lower latitudes. With anthropogenic emissions and climate forcing from a 1850-2000 climate model simulation, anthropogenic CO₂ accumulates at a similar rate and with a similar spatial distribution as estimated from observations. A hypothetical scenario for complete elimination of iron limitation generates maximal rates of uptake of atmospheric CO₂ of less than 1 PgC y⁻¹, or about 11% of 2004 industrial emissions. Even a ‘perfect’ future of sustained fertilization would have a minor impact on atmospheric CO₂ growth. In the long term, the onset of fertilization causes the ocean to take up an additional 77 PgC after several thousand years, compared with about 84 PgC thought to have occurred during the transition into the last glacial maximum due to iron fertilization associated with increased dust deposition.     

Deep ocean fluxes and their link to surface ocean processes and the biological pump

Intense studies of upper and deep ocean processes were carried out in the Northwestern Indian Ocean (Arabian Sea) within the framework of JGOFS and related projects in order to improve our understanding of the marine carbon cycle and the ocean’s role as a reservoir for atmospheric CO₂. The results show a pronounced monsoon-driven seasonality with enhanced organic carbon fluxes into the deep-sea during the SW Monsoon and during the early and late NE Monsoon north of 10°N. The productivity is mainly regulated by inputs of nutrients from subsurface waters into the euphotic zone via upwelling and mixed layer-deepening. Deep mixing introduces light limitation by carrying photoautotrophic organisms below the euphotic zone during the peak of the NE Monsoon. Nevertheless, deep mixing and strong upwelling during the SW Monsoon provide an ecological advantage for diatoms over other photoautotrophic organisms by increasing the silica concentrations in the euphotic zone. When silica concentrations fall below 2 μmol l⁻¹, diatoms lose their dominance in the plankton community. During diatom-dominated blooms, the biological pathway of uptake of CO₂ (the biological pump) appears to be more efficient than during blooms of other organisms, as indicated by organic carbon to carbonate carbon (rain) ratios. Due to the seasonal alternation of diatom and non-diatom dominated exports, spatial variations of the annual mean rain ratios are hardly discernible along the main JGOFS transect.Data-based estimates of the annual mean impact of the biological pump on the fCO₂ in the surface water suggest that the biological pump reduces the increase of fCO₂ in the surface water caused by intrusion of CO₂-enriched subsurface water by 50–70%. The remaining 30 to 50% are attributed to CO₂ emissions into the atmosphere. Rain ratios up to 60% higher in river-influenced areas off Pakistan and in the Bay of Bengal than in the open Arabian Sea imply that riverine silica inputs can further enhance the impact of the biological pump on the fCO₂ in the surface water by supporting diatom blooms. Consequently, it is assumed that reduced river discharges caused by the damming of major rivers increase CO₂ emission by lowering silica inputs to the Arabian Sea; this mechanism probably operates in other regions of the world ocean also.     

Origin and variability of downward biogeochemical fluxes on the Rhone continental margin (NW mediterranean)

A one year study of downward particle fluxes conducted in the northwestern Mediterranean Sea is presented. Two mooring lines equipped with sediment traps and current meters were deployed at around 1000 m depth on the northeastern continental slope of the Gulf of Lions, one inside the Grand-Rhône canyon and the other outside on the adjacent open slope. Mean total mass fluxes increased slightly with trap depth inside the canyon, a feature quite typical of fluxes in continental margin environments. The near-bottom trap inside the canyon collected more material than its counterpart deployed at equivalent depth on the open slope, indicating a preferential transport of material within the canyon. Major biogeochemical constituents (organic and inorganic carbon, opal, and siliciclastic residue) revealed a marked difference in particle composition between the sub-surface (80 m) and deeper traps, suggesting the existence of at least two sources of material. The two shallower traps showed a clear biological signal: flux peaks were related to periods of surface biological production, especially perceptible in summer and autumn. The particulate matter trapped at deeper levels in the canyon and on the open slope was characterized by a more stable composition with a major lithogenic contribution, originating from sedimentary material most probably resuspended on the upper- or mid-slope. The seasonal variability was dominated by the summer/winter alternation; the latter period was characterized by a weak stratification of the water column and an enhanced current variability favoring vertical exchanges. The present results are compared with those obtained previously in the Lacaze-Duthiers canyon on the southwestern side of the Gulf of Lions. The comparison shows strong differences between the NE entrance and the SW exit of the gulf, with respect to the general along-slope circulation of water masses, both in terms of intensity of particulate fluxes and transport processes.     

Coupling of benthic oxygen uptake and silica release: implications for estimating biogenic particle fluxes to the seafloor

A new approach to predict biogenic particle fluxes to the seafloor is presented, which is based on diffusive oxygen uptake and, in particular, opal fluxes to the seafloor. For this purpose, we used a recently published empirical equation coupling benthic silica to oxygen fluxes, and showing a clear negative correlation between Si and O₂ fluxes. Dissolution of biogenic silica mediated by aerobic microbial activity has been inferred at 24 sites along the African and South American continental margins. Based on the assumption that these findings hold essentially for the entire Southern Atlantic Ocean, we applied the silica to oxygen flux ratio to a basin-wide grid of diffusive oxygen uptake extracted from the literature. Assuming that the silica release across the sediment-water interface equals the particulate flux of biogenic opal to the seafloor, we estimated minimum opal rain rates. We combined these calculations with published relationships between aerobic organic carbon mineralization and dissolution rates of calcite above the hydrographical lysocline, thereby assessing the calcite rain rate and particulate organic carbon flux to the seafloor. The addition of the buried fraction completes our budget of biogenic particulate rain fluxes. The combination of such empirical equations provides a powerful and convenient tool which greatly facilitates future investigations of biogenic particle fluxes to the seafloor.     

Biological Pump in Northwestern North Pacific

The northwestern North Pacific is considered to be one of the most productive areas in the global ocean. Although the marginal zones along the Japanese and Kuril islands, Kamchatka Peninsula, and Aleutian Islands are certainly productive, recent studies do not always show high primary production values in the western subarctic gyre (WSG). In addition, a recent analysis of the biological pump in the WSG showed that, in contrast to what was previously reported, the vertical change of the particulate organic carbon flux with depth is large. Nevertheless, the biological pump in the northwestern North Pacific may function to draw down the partial pressure of CO₂ in the surface water because the ratio of the organic carbon flux to inorganic carbon flux (C_org/C_inorg), the export flux, and the export ratio from the surface water are higher than those in other oceans. This article also introduces recent research on changes to the biological pump that might have been caused by global warming. This revised version was published online in July 2006 with corrections to the Cover Date.     

南沙群岛珊湖礁潟湖垂直沉降颗粒物中主要元素的生物地球化学过程研究

本文首次报道用沉积物捕捉器（ＳＴ）研究南沙群岛珊瑚礁湖沉降颗粒物中主要元素垂直通量、垂直转移形态、再循环过程及垂直通量与表层海水温度的关系。结果显示,作为生物化学沉积标志的Ｃａ、Ｍｇ具有最高的垂直通量,达１．４和０．１ｇ／（ｍ２·ｄ）以上,作为生物富集标志的Ｂｒ、Ⅰ也有较高的垂直转移量;垂直转移形态的研究表明Ｎａ、Ｋ、Ｃａ、Ｍｇ、Ｓｒ主要以碳酸盐结合态向海底转移,其中Ｃａ、Ｍｇ、Ｓｒ占９９％以上,Ｆｅ、Ｉ、Ｂａ主要以铁锰氧化物结合态向海底输送,在垂直沉降颗粒物到达海底后,有相当部分的主要元素可再循环进入水体中,Ｂｒ、Ｉ、Ｋ、Ａｌ的绝大部分进入再循环,Ｍｇ、Ｎａ、Ｃｌ有一半左右进入再循环,Ｃａ、Ｓｒ、Ｂａ、Ｆｅ大部分被埋葬;Ｎａ等９种元素的垂直转移量随ＳＳＴ呈指数降低响应,对ＳＳＴ的敏感性Ｆｅ＞Ｂｒ＞Ｓｒ＞Ｃａ＞Ｎａ＞Ｃｌ＞Ｍｇ＞Ｉ＞Ａｌ,这再一次验证了ＣａＣＯ３随温度升高,其溶解度降低、化学沉积量增加这一自然界的普遍规律,表明在珊瑚礁海水的垂直沉降颗粒物中主要元素是作为珊瑚的重要成分与ＣａＣＯ３一同被沉积下来的,ＣａＣＯ３起到稀释剂的作用。     

Regional estimates of POC export flux derived from thorium-234 in the western Arctic Ocean

1Introduction CarboncyclingintheArcticOceanplaysanim- portantroletoglobalchange.Traditionally,marine productivityintheArcticOceanisthoughttobevery low,andthussomebiogeochemicalprocessessuchas particleexportandcyclingofnutrientsarenotsoac- tivebecauseofthembeingcoveredperenniallybyice, lowtemperatureandshorttimeofphotosynthesis (PlattandRao,1975).Afewpreviousestimatesof particulateorganiccarbon(POC)exportindicateda neglectablemagnitudeinthecentralArcticOcean (Baconetal.,1989).However,recen…     

南海表层沉积物与水柱中沉降颗粒物对比研究及其古环境再造意义

分析了南海62个表层沉积物样品中生源(有机质、碳酸钙和蛋白石)和非生源(岩源物质)组分的含量变化和分布特征,并以沉积学分区为基础,结合5个沉积物捕获器站位,将南海划分为N、C-NE、SW和S 4个区域,对比分析了各区表层沉积物和水柱中沉降颗粒物中各组分含量、沉积通量分布特征和变化,探讨了表层沉积物的输出生产力、沉降颗粒物的初级生产力及真光层下100 m输出生产力三者之间的对应关系.结果显示:南海4个海域表层沉积物中各组分平均含量多数低于沉降颗粒物中的平均含量,而碳酸钙、岩源物质的沉积通量却多数高于沉降颗粒物中的沉积通量,分析得出表层沉积物中各组分平均含量和沉积通量不仅受水柱中各组分输出量影响,还受到陆源物质输入、溶解作用和上层水体营养盐影响.南海表层沉积物中生源组分沉积通量大小对应其输出生产力的大小.但是,由于陆源有机质、生源颗粒侧向漂移的影响,表层沉积物的输出生产力大小分布并不完全对应沉降颗粒物的初级生产力大小分布,尽管南海真光层下100 m输出生产力与沉降颗粒物的初级生产力比值与世界大洋"f"比平均值基本一致,但是,明显低于表层沉积物的输出生产力大小,只有在沉降颗粒物的初级生产力较高区域,真光层下100 m输出生产力大小才最接近表层沉积物的输出生产力大小.     

Mesopelagic zone ecology and biogeochemistry – a synthesis

The mesopelagic zone is the oceanic region through which carbon and other elements must pass in order to reach deeper waters or the sea floor. However, the food web interactions that occur in the mesopelagic zone are difficult to measure and so, despite their crucial importance to global elemental cycles, are not very well known. Recent developments in technology and new approaches have advanced the study of the variability in and controls upon the distribution and diversity of organisms in the mesopelagic zone, including the roles of respiration, recycling, and repackaging of particulate and dissolved organic material. However, there are remarkably few syntheses of the ecology and biogeochemistry of the microbes and metazoa that permanently reside or habitually visit this ‘twilight zone’. Without this synthesis, it is difficult to assess the impact of ongoing changes in ocean hydrography and chemistry, due to increasing atmospheric carbon dioxide levels, on the biological carbon pump. This paper reviews what is known about the distribution of microbes and metazoa in the mesopelagic zone in relation to their activity and impact on global biogeochemical cycles. Thus, gaps in our knowledge are identified and suggestions made for priority research programmes that will improve our ability to predict the effects of climate change on carbon sequestration.     

The Western North Pacific Playing a Key Role in Global Biogeochemical Fluxes

The oceanic biogeochemical fluxes in the North Pacific, especially its northwestern part, are discussed to prove their importance on a global scale. First, the air-sea exchange processes of chemical substances are considered quantitatively. The topics discussed are sea salt particles transported to land, sporadic transport of soil dust to the ocean and its role in the marine ecosystem, the larger gas transfer velocity of CO₂ indicating the effect of bubbles, and DMS and greenhouse gases other than CO₂. Next, chemical tracers are utilized to reveal the water circulation systems in the region, which are the Pacific Deep Water including its vertical eddy diffusivity, the North Pacific Intermediate Water and the Japan Sea Deep Water. Thirdly, the particulate transport process of chemical substances through the water column is clarified by analyzing the distribution of insoluble radionuclides and the results obtained from sediment trap experiments. Fourthly, the northern North Pacific is characterized by stating the site decomposing organic matter and Si playing a key role in the marine ecosystem. Both are induced by the upwelled Pacific Deep Water. Fifthly, the oceanic CO₂ system related to global warming is presented by clarifying the distribution of anthropogenic CO₂ in the western North Pacific, and roles of the upwelled Pacific Deep Water and the continental shelf zone in the absorption of atmospheric CO₂. Finally, Mn and other chemical substances in sediments are discussed as recorders of the early diagenesis and indicators of low biological productivity during glacial ages in the northwestern North Pacific. It is concluded that the western North Pacific is characterized mainly by the Pacific Deep Water bringing nutrients to the northern North Pacific, located at the exit of the global deep water circulation and, therefore, the region plays a key role in the global biogeochemical fluxes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of CO<Subscript>2</Subscript> Enrichment on Marine Phytoplankton

Rising atmospheric CO₂ and deliberate CO₂ sequestration in the ocean change seawater carbonate chemistry in a similar way, lowering seawater pH, carbonate ion concentration and carbonate saturation state and increasing dissolved CO₂ concentration. These changes affect marine plankton in various ways. On the organismal level, a moderate increase in CO₂ facilitates photosynthetic carbon fixation of some phytoplankton groups. It also enhances the release of dissolved carbohydrates, most notably during the decline of nutrient-limited phytoplankton blooms. A decrease in the carbonate saturation state represses biogenic calcification of the predominant marine calcifying organisms, foraminifera and coccolithophorids. On the ecosystem level these responses influence phytoplankton species composition and succession, favouring algal species which predominantly rely on CO₂ utilization. Increased phytoplankton exudation promotes particle aggregation and marine snow formation, enhancing the vertical flux of biogenic material. A decrease in calcification may affect the competitive advantage of calcifying organisms, with possible impacts on their distribution and abundance. On the biogeochemical level, biological responses to CO₂ enrichment and the related changes in carbonate chemistry can strongly alter the cycling of carbon and other bio-active elements in the ocean. Both decreasing calcification and enhanced carbon overproduction due to release of extracellular carbohydrates have the potential to increase the CO₂ storage capacity of the ocean. Although the significance of such biological responses to CO₂ enrichment becomes increasingly evident, our ability to make reliable predictions of their future developments and to quantify their potential ecological and biogeochemical impacts is still in its infancy. This revised version was published online in July 2006 with corrections to the Cover Date.     

Distribution, partitioning and fluxes of dissolved and particulate organic C, N and P in the eastern North Pacific and Southern Oceans

Concurrent distributions of dissolved and suspended particulate organic carbon (DOC and POC_susp), nitrogen (DON and PON_susp) and phosphorus (DOP and POP_susp), and of suspended particulate inorganic phosphorus (PIP_susp), are presented for the open ocean water column. Samples were collected along a three-station transect from the upper continental slope to the abyssal plain in the eastern North Pacific and from a single station in the Southern Ocean. The elemental composition of surface sedimentary organic matter (SOM) was also measured at each location, and sinking particulate organic matter (POM_sink) was measured with moored sediment traps over a 110-d period at the abyssal site in the eastern North Pacific only. In addition to elemental compositions, C : N, C : P and N : P ratios were also calculated. Surface and deep ocean concentrations of dissolved organic matter (DOM) and inorganic nutrients between the two sites displayed distinct differences, although suspended POM (POM_susp) concentrations were similar. Concentrations of DOM and POM_susp displayed unique C, N and P distributions, with POM_susp concentrations generally about 1–2 orders of magnitude less than the corresponding DOM concentrations. These differences were likely influenced by different biogeochemical factors: whereas the dissolved constituents may have been influenced more by the physical regime of the study site, suspended particulate matter may have been controlled to a greater extent by biological and chemical alteration. Up to 80% of total particulate P in POM_susp, POM_sink and SOM consisted of PIP. For all organic matter pools measured, elemental ratios reveal that organic P is preferentially remineralized over organic C and organic N at both sites. Increases in C : P and N : P ratios with depth were also observed for DOM at both sites, suggesting that DOP is also preferentially degraded over C and N as a function of depth. A simple one-dimensional vertical eddy diffusion model was applied to estimate the contributions of dissolved and suspended particulate organic C, N and P fluxes from the upper mixed layer into the permanent thermocline. Estimated vertical DOM fluxes were 28–63% of the total organic matter fluxes; POM_susp and POM_sink fluxes were 8–20 and 28–52% of the total.     

The particle fluxes in sediment traps from Niulang Guyot area in the Northwest Pacific Ocean

The flux of settling particles in the ocean has been widely explored since 1980s due to its important role in biogenic elements cycling, especially in the transport of particulate organic carbon (POC) in the deep sea. However, research in the seamount area of the oligotrophic subtropical Northwest Pacific Ocean is lacking. In this work, two sediment traps were deployed at the foot and another two at the hillside of Niulang Guyot from August 2017 to July 2018. The magnitude and composition of particle fluxes were measured. The main factors influencing the spatial variations of the fluxes were evaluated. Our results indicated a low particulate flux from Niulang Guyot area in the Northwest Pacific Ocean, reflecting low primary productivity of the oligotrophic ocean. The total mass flux (TMF) decreased from 2.57 g/(m2·a) to 0.56 g/(m2·a) with increasing depth from 600 m to 4 850 m. A clear seasonal pattern of TMF was observed, with higher flux in summer than that in winter. The peak flux of 26.52 mg/(m2·d) occurred in August at 600 m, while the lowest value of 0.07 mg/(m2·d) was shown in February at 4 850 m. The settling particles at the deep layers had similar biochemical composition, with calcium carbonate (CaCO₃) accounting for up to 90%, followed by organic matter and opal, characteristics of Carbonate Ocean. The POC flux decreased more rapidly in the twilight layer because of faster decomposition, remineralization, and higher temperature. A small fraction of POC was transported into the deep ocean by biological pump. Particle fluxes were mainly controlled by the calcareous ballasts besides the primary productivity of the surface water. The advection may be another important factor affecting the flux in the seamount area. The combination of settled matters rich in foraminiferal tests with topography and currents may be the reason for regulating the local abundance of benthos on seamounts. Our results will fill in the knowledge gap of sedimentation flux, improve the understanding of ecosystem in Niulang Guyot area, and eventually provide data support for the optimization of regional ecological modeling.     

生物要素的海洋生物地球化学过程研究进展

新学科的诞生是社会发展的需要,人类社会发展到今天,由于人类面临的资源与环境问题,使占全球面积71%的海洋成为21世纪开发的重点领域。然而,各成体系的海洋化学、海洋生物、海洋地质和海洋水文,已难以适应认识和解决当前面临的全球变化问题的需要。80年代初,随着国际地圈生物圈计划(IGBP)、全球海洋通量联合研究(JGOFS)、全球海洋生态系统动力学(GLOBEC)、全球海洋真光层研究(GOEZS)、海岸带陆海相互作用(LOICZ)等重大国际合作计划的兴起,处于这些学科交叉点上的海洋生物地球化学这新的分支学科应运而生,至90年代,这一边缘交又研究方向已成为海洋学研究的前沿领域。 我国的海洋生物地球化学研究虽起步较晚,但已取得飞速发展。至今,已开展实施了渤海生态系统动力学、东海海洋通量、台湾海峡生源要素生物地球化学过程、南海碳通量、南沙群岛珊瑚礁生态系物质循环等一系列重点项目的研究,强有力地推动了这一边缘交叉学科的发展。 海洋生物地球化学是利用化学、地质、生物、物理的观点综合研究海洋中物质循环的过程与规律,突出的特点是研究生物作用下的地球化学过程,研究的主要对象是生源要素(C,N,P,S,Si等)及与生物过程有关的其他元素。 本文从真光层内生源要素的循环、海水中颗粒物的生物地球化学过程、沉积物-海水界面过程中的生源要素,以及微型生物在生源要素的海洋生物地球化学循环中的作用等方面阐述了生源要素的海洋生物地球化学过程研究进展,以期推进我国该领域研究水平的提高。