南海北部生源要素的垂直输运和保存及其与东太平洋的对比研究

通过对南海北部夏、冬两个季节的生源要素垂直输运剖面和时间系列沉积物捕获器的测量资料进行综合研究表明:南海北部颗粒物质主要是由钙质生物壳、生物硅、海洋浮游生物的有机质以及岩源物质组成,颗粒物质通量在1 000 m处大约为90.0 mg/(m2·d);研究还表明颗粒有机碳在进入沉积物保存之前被大量溶解,南海北部来自底层顺坡搬运的有机碳远大于垂直沉降;与开阔大洋(东太平洋海域)的对比研究表明,边缘海对于季节的变化更加敏感,而东太平洋调查区位于热带赤道高生产力带,生物作用十分明显,其海洋生物呼吸和物质转移同样也较活跃.     

The investigation on particulate organic carbon fluxes with disequilibria between thorium-234 and uranium-238 in the Prydz Bay, the Southern Ocean

Dissolved and particulate thorium-234, particulate organic carbon in the upper 150 m of water columns from five stations in the Prydz Bay, the Southern Ocean were determined during the 22nd Chinese National Antarctic Research Expedition （from November 2005 to March 2006 ）. The disequilibria between thorium-234 and its parent uranium-238 in upper layer was used to derive the averaged residence time of thorium-234, which decreased along with the latitude to the south and a minimum value, 1 - 8 d for particulate thorium-234 and 29 - 48 d for dissolved thorium-234, appeared at the medium latitude station, and the export fluxes of thorium-234 were calculated too and ＇a maximum value, 0. 35 -0. 63 Bq/（m^3 · d） for the particulate thorium-234 and 0. 44 -0. 65 Bq/ （m^3 ·d） for the dissolved thorium-234, appeared at the same station. The export fluxes of particulate organic carbon at different water columns were derived by two methods with irreversible scavenging model, and the averaged values were 104. 7 mmol/ （ m2 · d ） （ E method） and 120. 6 mmol/（ m2·d ） （ B method ）, respectively, indicating that a relatively high new production would exist in summer in the Prydz Bay where it will play a potential significant role in sequestering the absorption CO2 to deeper ocean.     

白令海颗粒有机物碳、氮同位素组成及其生物地球化学意义

Stable carbon and nitrogen isotopic composition of particulate organic matter(POM) were measured for samples collected from the Bering Sea in 2010 summer. Particulate organic carbon(POC) and particulate nitrogen(PN) showed high concentrations in the shelf and slope regions and decreased with depth in the slope and basin, indicating that biological processes play an important role on POM distribution. The low C/N ratio and heavy isotopic composition of POM, compared to those from the Alaska River, suggested a predominant contribution of marine biogenic organic matter in the Bering Sea. The fact that δ13C and δ15N generally increased with depth in the Bering Sea basin demonstrated that organic components with light carbon or nitrogen were decomposed preferentially during their transport to deep water. However, the high δ13C and δ15N observed in shelf bottom water were mostly resulted from sediment resuspension.     

Temporal variations of dissolved and particulate Th at a coastal station of the northern Adriatic Sea

Water–particle interactions, particle behaviour and short-time scale variability were assessed at a coastal station adjacent to the Emilia Romagna Region (Adriatic Sea) using dissolved and particulate ²³⁴Th analyses. The water column was sampled six times between March and September 1997. Measurements showed that ²³⁴Th is actively scavenged by particles but the dissolved fraction is always prevalent. Changes in hydrological conditions affect to some degree thorium activities and residence times. Dissolved thorium inventories slowly increased from May to July, then decreased in August, and increased again in September. In July, the formation of a sharp pycnocline associated with low productivity led to high dissolved and very low particulate ²³⁴Th activities due to inefficient scavenging. The presence of mucilaginous aggregates, observed in both August and September, may have played a role in scavenging of thorium. In September at 16 m depth, the highest ²³⁴Th particulate activity of the study period was measured, probably due to the presence of mucilage. However, the thorium deficit was scarce, due to the small sinking velocity of these aggregates. Both steady-state and non-steady state models were used to calculate residence times for the whole water column and its topmost part (10 m) obtaining strictly comparable results. Residence times in the whole water column are small, ranging from 15 to 45 and from 0.5 to 24 d for dissolved and particulate thorium, respectively.     

Contrasting behaviors of 210Po, 210Pb and 234Th in the East China Sea during a severe red tide: Enhanced scavenging and promoted fractionation

210Po, 210Pb, and 234Th were determined in water columns of the East China Sea (ECS) to investigate their biogeochemical behaviors during a severe red tide event. Dissolved 210Po, 210Pb, and 234Th accounted for large fractions of the total phases. The abnormally high concentrations of dissolved 210Pb were observed. Partition behaviors of these radionuclides were influenced by particle content effect and particle composition based on distribution coefficient (K_d) vs. total suspended matter (TSM) content and K_d vs. ratios of particulate organic carbon and total suspended matter contents (POC/TSM content ratios). The peaks of mass specific activities of 210Po, 210Pb, and 234Th indicated that degraded particles could have an intensified enrichment ability for radionuclides compared with the surficial suspended matters. Fractionation factor of 210Po and 210Pb (F_Po/Pb) (>1) and fractionation factor of 210Po and 234Th (F_Po/Th) (>1) were much higher at algal blooming regions than that at non-blooming stations, indicating that algal blooms promoted the fractionation of 210Po against 210Pb and 234Th, and proving that 210Po exhibited a stronger affinity for biogenic particles than 210Pb and 234Th when POC content increased in the sea. POC/210Po, POC/210Pb and POC/234Th ratios (content/activity ratios) sharply decreased with depth in both algal bloom and non-bloom stations. The outbreak of algal bloom promoted the complexity of suspended particles and increased the variability of POC/tracer ratios (content/activity ratios) in the different depth of the shallow seas. More considerations should be taken to the difficulty of the selection of export interface and the suitable tracers when algal blooming occurs.     

An in-situ analysis and measurement of thorium-234, uranium isotopes in seawater

A low-level β counting-α spectrum apparatus used for the detection of the β radiation of thorium-234 and α spectrum of thorium-228 simultaneously and an easy operating procedure for the enrichment, radiochemical separating, sampling and measurement of thorium-234 and uranium-238 in the ocean are developed based on the requirements of analyzing export productivity in the euphotic zone via thorium-234-uranium-238 radioactivity disequilibrium. The detecting efficiency both of β and α radiation is higher than 20%. The background of β radiation is less than 0.5 min-1, and the energy resolution of α detector is better than 1%. Total recycle ratio of thorium-234 is about 75%. Using the above apparatus and procedure, the radioactivities of dissolved thorium-234 and uranium-238, particle thorium-234 and uranium-238 in seawater of the South China Sea, the Southern Ocean and the Arctic Ocean were analyzed.     

Particulate organic carbon export flux by 234Th/238U disequilibrium in the continental slope of the East China Sea

234Th is widely used to quantify the magnitude of upper ocean particulate organic carbon(POC)export in oceans.In the present work,the rates of particulate organic carbon export were measured based on the distribution patterns of234Th/238U disequilibrium in the water column within the continental slope of the East China Sea(ECS)during May 2011.The profiles of particulate and dissolved234Th activities at all three stations showed a relative deficit with respect to238U in the upper 100 m of the water column.The dissolved234Th scavenging rates and the particulate234Th removal rates and their residence times were calculated by a one-dimensional steady state model.The results showed that the dissolved234Th scavenging rates and the particulate234Th removal rates ranged from 12.4–61.4 dpm/(m3·d)andfrom3.8–21.8 dpm/(m3·d),respectively.The residence times of dissolved and particulate234Th were in the range of 3.4–158 d and 63.7–96.5 d,respectively.Combined with the measurement of POC/234Th ratios of suspended particles,POC export flux(calculated by carbon)from the euphotic zone was estimated in the study region,which ranged from 4.14–14.7 mmol/(m2·d),withanaverageof8.21mmol/(m2·d),occupying35%oftheprimeproductivity in the study area.The results of this study can provide new information for better understanding the carbon biogeochemical cycle within the continental slope of the ECS.     

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.     

东海陆架表层水体有机与无机悬浮体的季节分布特征

利用2011年春季(5-6月)、2009年夏季(8月)、2010年秋季(11-12月)和2009 年冬季(12月一次年1月)4个航次实测的悬浮体质量浓度资料,分析了东海陆架表层水体总悬浮体、有机悬浮体和无机悬浮体质量浓度的季节分布特征。结果表明,东海陆架表层水体总悬浮体质量浓度冬半年高于夏半年,等值线基本平行于岸线,在浙江沿岸29°N附近有一浑水舌向东南方向延伸,常年存在2个高值中心和2个次高值中心。有机悬浮体质量浓度则为夏半年高于冬半年,存在2个高值中心和2个次高值中心,季节变化显著。无机悬浮体质量浓度分布趋势相似于总悬浮体质量浓度,但整体轮廓线向近岸收缩约0.5°,常年存在2个高值中心和1个次高值中心。有机悬浮体占总悬浮体百分比按季节从高到低依次为春季、夏季、冬季和秋季,其中长江口、杭州湾外近海海域和黑潮区为东海有机悬浮体百分含量高值区。     

Upper ocean export of particulate organic carbon and biogenic silica in the Southern Ocean along 170°W

Upper-ocean fluxes of particulate organic carbon (POC) and biogenic silica (bSi) are calculated from four US JGOFS cruises along 170°W using a thorium-234 based approach. Both POC and bSi fluxes exhibit large variability vs. latitude during the seasonal progression of diatom dominated blooms. POC fluxes at 100 m of up to 50 mmol C m⁻² d⁻¹ are found late in the bloom, and farthest south near the Ross Sea Gyre. Biogenic Si fluxes also peak late in the bloom as high as 15 mmol Si m⁻² d⁻¹, but this flux peak occurs at a different latitude, just south of the Antarctic Polar Front (APF), which is centered around 60°S along this cruise track. The ratios of both POC and bSi export relative to their production rates are large, suggesting an efficient biological pump at these latitudes. The highest relative bSi/POC flux ratios at 100 m are found just south of the APF, coincident with a bSi/POC flux peak seen in 1000 m traps during this same program by Deep-Sea Research II (Honjo et al., Deep-Sea Research II 47, 3521–3548). These data suggest that efficient export at these latitudes can support the high accumulation rates of bSi found in the sediments under and south of the APF, despite the generally low biomass and productivity levels in this region.     

Tracing suspended organic nitrogen from the Yangtze River catchment into the East China Sea

Total suspended matter was collected along the Yangtze River (Changjiang) and in the East China Sea in April to May and in September 2003, respectively, to study origin and fate of particulate organic nitrogen. Concentrations of particulate organic carbon (POC), nitrogen (PN) and hydrolyzable particulate amino acids (PAA; d- and l-enantiomers) were higher in the Yangtze Estuary than in the river and decreased offshore towards the shelf edge. In the coastal area, higher values of PAA were observed in the surface layer than in the bottom water. Stable carbon isotope ratios (δ¹³C) of POC increased from − 24.4‰ in the river to values around − 21‰ on the East China Sea Shelf. Dominant amino acids were aspartic acid + aspartine (Asx), glutamic acid + glutamine (Glx), glycine, alanine and serine. The proportions of Asx, Glx and isoleucine were higher in the marine than in the riverine samples contrary to the distributions of glycine, alanine, threonine and arginine. The proportions of d-amino acids were highest in the riverine suspended organic matter (6% of PAA) decreasing towards the shelf edge (1.5% of PAA). d-arginine, not reported in natural aquatic samples so far, was the most abundant d-amino acid in the river. The amino acid composition of the particulate organic matter (POM) in the Yangtze River indicates an advanced stage of degradation of POM. Highly degraded organic matter from soils is probably a main source of POM in the Yangtze River, but the relatively high δ¹³C values and low C/N ratios (7.7 ± 1.6) also indicate contribution from anthropogenic sources. The degraded riverine material was a dominant organic matter source in the estuary, where aquatic primary production had only a small overall contribution. In the East China Sea, gradual settling of riverine organic matter and the addition of fresher phytoplankton impacted the amino acid composition and δ¹³C values, and on the outer shelf relatively fresh phytoplankton-derived organic matter dominated.     

Biogeochemical impacts due to mesoscale eddy activity in the Sargasso Sea as measured at the Bermuda Atlantic Time-series Study (BATS)

A comparison of monthly biogeochemical measurements made from 1993 to 1995, combined with hydrography and satellite altimetry, was used to assess the impacts of nine eddy events on primary productivity and particle flux in the Sargasso Sea. Measurements of primary production, thorium-234 flux, nitrate+nitrite, and photosynthetic pigments made at the US JGOFS Bermuda Atlantic Time-series Study (BATS) site were used. During the 3 years of this study, four out of six high thorium-234 flux events occurred during the passage of an eddy. Primary production nearly as high as the spring bloom maximum was observed in two mode-water eddies (May 1993 and July 1995). The 1994 spring bloom at BATS was suppressed by the passage of an anticyclone. Distinct phytoplankton community shifts were observed in mode-water eddies, which had an increased percentage of diatoms and dinoflagellates, and in cyclones, which had an increased percentage of Synechococcus. These variations in species composition within mode-water eddies and cyclones may be associated with the ages of the sampled eddies, and/or differences in physical, chemical, and biological factors in these two distinct eddy types. In general, eddies that were 1–2 months old elicited a large biological response; eddies that were 3 months old may show a biological response and were accompanied by high thorium flux; eddies that were 4 months old or older did not show a biological response or high thorium flux. A conceptual model depicting temporal changes during eddy upwelling, maturation, and decay can explain the observations in all seven upwelling eddies present in the time-series investigated herein.     

Role of colloidal material in the removal of 234Th in the Canada basin of the Arctic Ocean

The phase partitioning of ²³⁴Th between dissolved (<10-kiloDalton, kD), colloidal (10 kD—0.4 μm), and particulate (⩾0.5 μm) matter across a horizontal transect, from a coastal station to the deep Canada Basin, and a vertical profile in the deep Canada Basin of the western Arctic Ocean was investigated. Concentrations of suspended particulate matter (SPM), dissolved, colloidal and particulate organic carbon, particulate organic nitrogen and nutrients (silicate, phosphate and nitrate) were also measured to assess transport and scavenging processes.Total ²³⁴Th (colloidal+particulate+dissolved) indicated deficiencies relative to secular equilibrium with its parent, ²³⁸U in the upper 100 m, which suggests active scavenging of ²³⁴Th onto particle surfaces. In contrast, at depths >200 m, general equilibrium existed between total ²³⁴Th and ²³⁸U. The inventory of SPM and the specific activity of particulate ²³⁴Th in the Canada Basin was about an order of magnitude higher than the profile reported for the Alpha Ridge ice camp station. This higher concentration of SPM in the southwestern Canada Basin is likely derived from ice-rafted sedimentary particles. Inventories of nutrients, and dissolved organic carbon and nitrogen in the upper 100 m of the Canada Basin are comparable to the other estimates for the central Arctic Ocean. Comparison of the mass concentrations of colloidal and filter-retained particulate matter as well as the activity of ²³⁴Th in these phases indicates that only a very small component of the colloidal material is actively involved in Th scavenging. Lower values of the conditional partition coefficient between the colloidal and dissolved phase indicate that the Arctic colloids are less reactive than colloidal material from other regions. The conditional partition coefficient between the filter-retained and dissolved phases (K_f) is generally higher than that for other regions, which is attributed to the higher complexation capacity of glacio-marine sedimentary particles in these waters. The ²³⁴Th-derived export of POC for the shelf and deep Canada Basin ranges between 5.6 and 6.5 mmol m⁻² d⁻¹, and is in agreement with other estimates reported for the central Arctic Ocean and Beaufort Sea.     

Thorium speciation in seawater

Since the 1960s, thorium isotopes occupy a special place in the oceanographer's toolbox as tracers for determining rates and mechanisms of oceanic scavenging, particle dynamics, and carbon fluxes. Due to their unique and constant production rates from soluble parent nuclides of uranium and radium, their disequilibrium can be used to calculate rates and time scales of sinking particles. In addition, by ratio-ing particulate ²³⁴Th (as well, in principle, other Th-nuclides) to carbon (and other elements), and linking this ratio to the parent–daughter disequilibrium in the water column, it is possible to calculate fluxes of carbon and other elements. Most of these applications are possible with little knowledge of the dissolved chemical properties of thorium, other than its oxidation state (IV) and tendency to strongly sorb to surfaces, i.e., its “particle- or surface-activity”. However, the use of any tracer is hindered by a lack of knowledge of its chemical properties. Recent observations in the variability of carbon to ²³⁴Th ratios in different particle types, as well as of associations of Th(IV) with various marine organic biomolecules has led to the need for a review of current knowledge and what future endeavors should be taken to understand the marine chemistry of thorium.     

Hypoxia in the East China Sea: one of the largest coastal low-oxygen areas in the world

Anoxia and hypoxia have been widely observed in estuarine and coastal regions over the past few decades; however, few reports have focused on the East China Sea (ECS). In June and August 2003, two cruises sampled at stations covering almost the entire shelf of the ECS to examine hypoxic events and their potential causes. In August, DO concentrations <2-3 mg l(-1) covered an area estimated at greater than 12,000 km(2) (or 432 km(3) volume). In contrast, water column DO concentrations exceeded 4 mg l(-1) throughout most of the shelf region. A sharp density gradient was observed under the mixed layer in August, restricting vertical re-aeration across this strong pycnocline. Oxygen depletion events, such as that described here for the ECS shelf, are fueled by decomposition of newly produced marine and river-borne biogenic substances (as well as older residual organic matter) deposited to the bottom waters.     

悬浮泥沙在长江口铀非保守行为中的重要作用

利用高精度的电感耦合等离子体质谱仪对2014年1月长江口表层水中溶解铀浓度及其234U/238U比值、2013年3月长江口表层沉积物中各矿物组分的铀含量及其234U/238U比值进行了测定,研究了其空间分布特征和影响因素。结果表明:除了长江径流和海水之外,长江口还有其他的溶解铀来源。水体中过剩铀与悬浮颗粒物浓度呈现显著相关性（r2=0.96）。对长江口表层沉积物进行的序列提取实验进一步表明,水体中悬浮颗粒物或沉积物中可解吸态和碳酸钙结合态铀可以在河口区域释放进入水体,而铁锰氧化物和有机物结合铀比较稳定,不受河口区混合过程的影响。每千克颗粒物或沉积物能够释放约2 μmol颗粒态铀,使其转化为溶解态。然而,铁氢氧化物和细颗粒物的絮凝吸附作用也可使溶解铀同时从河口水体中清除。在低盐度区,铀的清除和添加过程速率相近,使溶解铀呈现暂时的"伪保守"现象:颗粒态释放的铀具有明显低的234U/238U比值,导致水体的234U/238U低于保守混合值。在中高盐度区域,溶解铀呈现明显的富集现象。但是由于水相和颗粒相中的铀交换,可释放颗粒态铀的234U/238U接近溶解铀的234U/238U比值,从而导致水体的234U/238U比值呈现出保守性。长江口颗粒物的铀释放通量为（3.48±0.41）×105 mol/a,约占输入的总颗粒态铀通量（1.80±0.17）×106 mol/a的19.3%。长江口输入东海的溶解铀总通量（河流溶解态铀与河口添加铀之和）为（2.68±0.13）×106 mol/a,约为世界河流入海铀通量的11.7%。     

Particulate barium fluxes on the continental margin: a study from the Alboran Sea (Western Mediterranean)

Particulate biogenic barium (bio-Ba) fluxes obtained from three instrumented arrays moored in the Alboran Sea, the westernmost basin in the Mediterranean Sea, are presented in this study. The mooring lines were deployed over almost 1 year, from July 1997 to May 1998, and were equipped with sediment traps at 500–700 m depth, 1000–1200 m depth and 30 m above the seafloor (1000–2200 m). The results obtained support the growing body of evidence that the relationship between particulate bio-Ba and Corg throughout the water column in margin systems is clearly different from this relation in the open ocean. In the Alboran Sea, the annual averaged bio-Ba fluxes range from 0.39 to 1.07 μmol m⁻² day⁻¹, with mean concentrations of 1.31–1.69 μmol g⁻¹ and bio-Ba/Corg ratios lower than in the open ocean. The low bio-Ba values obtained also indicate that calculating bio-Ba is extremely sensitive to the detrital Ba/Al ratio of each sample. The lithogenic Ba fraction in the Alboran Sea continental margin area contributes between 24% and 85% of the total Ba. Increased bio-Ba export efficiency was observed after periods of high primary productivity and suggests that the processes limiting the bio-Ba formation in the study area relate to settling dynamics of organic matter aggregates. Furthermore, the ballasting effect of the abundant lithogenic and carbonate particles may limit decomposition of organic matter aggregates and enhance the transfer of particles rich in Corg and relatively poor in bio-Ba to the deep seafloor. Lateral input of freshly sedimented biogenic material, including particulate bio-Ba, has been observed on the lower continental slope in the western Alboran Sea. These observations emphasize that the use of the bio-Ba as a proxy of export productivity from the surface ocean must be used cautiously in highly dynamic environments such as those in the Alboran Sea.     

Distribution of 210Po and export of organic carbon from the euphotic zone in the southwestern East Sea (Sea of Japan)

The distribution of the natural radionuclide ²¹⁰Po in the water column along a horizontal transect of the continental shelf, slope and deep basin regions of the East Sea (Sea of Japan), a marginal sea of the Northwest Pacific Ocean, was investigated, and its behavior is described here. The settling fluxes of particulate ²¹⁰Po in the deep basin along with ²¹⁰Pb, ²³⁴Th and biogenic matter were also determined. ²¹⁰Po inventories in the water column were observed to decrease from winter to summer in all stations, probably due to increased influx of ²¹⁰Po-poor Kuroshio Water of the Northwest Pacific Ocean during summer. Vertical profiles of dissolved and particulate ²¹⁰Po along with the settling fluxes of particulate ²¹⁰Po in the deep basin station have enabled us to evaluate temporal variations and residence times of ²¹⁰Po. In the slope and basin, activities of dissolved ²¹⁰Po generally decreased from the surface to the bottom water, with maximum activity just below the subsurface chlorophyll a maximum at 50–75 m depth in spring and summer. These subsurface peaks of dissolved ²¹⁰Po activity were attributed to the release of ²¹⁰Po from the decomposition of ²¹⁰Po-laden biogenic particulate organic matter. In the deep basin, despite the decrease in total mass flux, the sinking flux of particulate ²¹⁰Po was higher in the deeper trap (2000 m) than in the shallower one (1000 m), probably due to scavenging of dissolved ²¹⁰Po from the water column during particle descent and/or break-down of ²¹⁰Po-depleted particulate matter between 1,000 m and 2,000 m depths. In general, the ratios of the particulate phase to the dissolved phase of ²¹⁰Po (K_d) increased with depth in the slope and basin stations. ²¹⁰Po removal from the water column appears to depend on the primary productivity in the upper waters. There is an inverse relationship between K_d and suspended particulate matter (SPM) concentration in the water column. From the ²¹⁰Po activity/chlorophyll a concentration ratios, it appears that sinking particles arriving at 1000 m depth were similar to those in the surface waters.     

南海北部海洋雾状层特征及影响因素初步研究

在粤东上升流区和南海北部陆架陆坡区共选取7条断面,通过分析水体的温度、盐度、密度、浊度、叶绿素浓度特征和悬浮体现场粒度平均粒径、体积浓度特征等,初步研究了南海北部海洋雾状层的特征及其受控机制。研究发现粤东上升流区底部雾状层普遍发育,在个别站位存在表层雾状层,高能的近岸浪流作用和来自港湾、河流的泥沙为表层雾状层和底部雾状层提供物源;南海北部陆架陆坡区底部雾状层也普遍发育,在珠江口外的内陆架和外陆架陆坡区表层雾状层比较常见,陆坡区中层雾状层比较发育,本区雾状层的物源主要来自珠江和台湾岛西南部河流的入海泥沙、海底沉积物以及生源颗粒物。南海北部底部雾状层的强度和扩散范围主要受水动力条件、河流入海物质的扩散和底质再悬浮等控制。     

Investigating the effect of ballasting by CaCO3 in Emiliania huxleyi, II: Decomposition of particulate organic matter

The quantitative relationship between organic carbon and mineral contents of particles sinking below 1800 m in the ocean indicates that organisms with mineral shells such as coccolithophores are of special importance for transporting carbon into the deep sea. Several hypotheses about the mechanism behind this relationship between minerals and organic matter have been raised, such as mineral protection of organic matter or enhanced sinking rates through ballast addition. We examined organic matter decomposition of calcifying and non-calcifying Emiliania huxleyi cultures in an experiment that allowed aggregation and settling in rotating tanks. Biogenic components such as particulate carbon, particulate nitrogen, particulate volume, pigments, transparent exopolymer particles (TEP), and particulate amino acids in suspended particles and aggregates were followed over a period of 30 d. The overall pattern of decrease in organic matter, the amount of recalcitrant organic matter left after 30 d, and the compositional changes within particulate organic matter indicated that cells without a shell are more subject to loss than calcified cells. It is suggested that biogenic calcite helps in the preservation of particulate organic matter (POM) by offering structural support for organic molecules. Over the course of the experiment, half the particulate organic carbon in both calcifying and non-calcifying cultures was partitioned into aggregates and remained so until the end of the experiment. The partial protection of particulate organic matter from solubilization by biominerals and by aggregation that was observed in our experiment may help explain the robustness of the relationship between organic and mineral matter fluxes in the deep ocean.