The behaviour of dissolved Cd, Co, Zn, and Pb in North Atlantic near-surface waters (30°N/60°W–60°N/2°W)

In September 1993 (M26) and June/July 1996 (M36), a total of 239 surface samples (7 m depth) were collected on two transects across the open Atlantic Ocean (224 samples) and northwest European shelf edge area. We present an overview of the horizontal variability of dissolved Cd, Co, Zn, and Pb in between the northwest and northeast Atlantic Ocean in relation to salinity and the nutrients. Our data show a preferential incorporation of Cd relative to P in the particulate material of the surface ocean when related to previously published parallel measurements on suspended particulate matter from the same cruise. There is a good agreement with results recently estimated from a model by Elderfield and Rickaby (Nature 405 (2000) 305), who predict for the North Atlantic Ocean a best fit for α_Cd/P=[Cd/P]_POM/[Cd/P]_SW of 2.5, whereas the approach of our transect shows a α_Cd/P value of 2.6. The Co concentrations of our transects varied from <5 to 131 pmol kg⁻¹, with the lowest values in the subtropical gyre. There were pronounced elevations in the low-salinity ranges of the northwest Atlantic and towards the European shelf. The Co data are decoupled from the Mn distribution and support the hypothesis of marginal inputs as the dominant source. Zinc varied from a minimum of <0.07 nmol kg⁻¹ to a maximum of 1.2 and 4.8 nmol kg⁻¹ in regions influenced by Labrador shelf or European coastal waters, respectively. In subtropical and northeast Atlantic waters, the average Zn concentration was 0.16 nmol kg⁻¹. Zinc concentrations at nearly three quarters of the stations between 40°N and 60°N were <0.1 nmol kg⁻¹. This suggests that biological factors control Zn concentrations in large areas of the North Atlantic surface waters. The Pb data indicated that significant differences in concentration between the northwest and northeast Atlantic surface waters presently (1996) do not exist for this metal. The transects in 1993 and 1996 exhibited Pb concentrations in the northeast Atlantic surface waters of 30 to 40 pmol kg⁻¹, about a fifth to a quarter of the concentrations observed in 1981. This decline is supported by our particle flux measurements in deep waters of the same region.     

Vertical and horizontal distribution of fluorescent dissolved organic matter in the Southern Ocean

The vertical and horizontal distribution of fluorescent dissolved organic matter (FDOM), determined by fluorescence intensity at 320 nm excitation and 420 nm emission, were clarified in nine stations on two transects at the Southern Ocean, including a subtropical, subantarctic, polar frontal and Antarctic zone. All vertical profiles of fluorescence intensity showed that levels were lowest in the surface waters, increased with increasing the depth in mid-depth waters ( 2000 m), and then stayed within a relatively narrow range from there to the bottom. Such vertical profiles of FDOM were similar to those of nutrients, but were adverse to dissolved oxygen. In water columns below the temperature-minimum subsurface water (dichothermal waters) in the Antarctic zone and below the winter mixed layer in the other zones, we determined the relationships of fluorescence intensity to concentrations of nutrients and apparent oxygen utilization (AOU) over the entire area of the present study, and found significant linear correlations between the levels of fluorescence intensity and nutrient concentrations (r =  0.70 and 0.71 for phosphate and nitrate + nitrite, respectively) and AOU (r = 0.91). From the strong correlation coefficient between fluorescence intensity and AOU, we concluded that FDOM in the Southern Ocean is formed in situ via the biological oxidation of organic matter. The regeneration of the nutrients/consumption of the oxygen/formation of FDOM was active in mid-depth waters. However, the correlations between fluorescence intensities and nutrients and AOU were different in the mid-depth water masses, Subantarctic Mode Water (SAMW), and Antarctic Intermediate Water (AAIW), indicating that the sources of organic matter responsible for FDOM formation were different. A considerable amount of FDOM in the SAMW is thought to be produced by the remineralization of DOM in addition to sinking particulate organic matter, while DOM is less responsible for FDOM formation in the AAIW.     

2002年夏季南极普里兹湾及其邻近海域浮游植物现存量、初级生产力粒级结构和新生产力研究

2002年1～2月,在南极普里兹湾及其北部海区对浮游植物生物量、优势种类组成、细胞丰度、初级生产力和新生产力的观测结果表明,叶绿素a浓度、初级生产力和新生产力的高值均出现在湾内及湾口陆架区,并且远高于陆坡和深海区.湾内和湾口陆架区表层叶绿素a浓度均高于1 mg/m3,平均为(2.34±0.85)mg/m3,而陆坡区和深海区平均只有(0.19±0.14)和(0.15±0.05)mg/m3.湾内和陆架区平均初级生产力[(355.8±192.1)mg/(m2·d)]高于陆坡区[(82.0±20.8)mg/(m2·d)]和深海区[(100.5±83.4)mg/(m2·d)].在陆坡和深海区初级生产力的粒级结构以微微型浮游生物(<2 μm)对初级生产力的贡献最大(分别为49.6%和46.2%),湾内和陆架区则以小型浮游生物(为20～280 μm)的贡献为主(66.2%).在湾内和湾口陆架区同时具有较高的新生产力和再生生产力.     

Size fractionated biomass and productivity of phytoplankton and new production in the Prydz Bay and the adjacent Indian sector of the Southern Ocean during the austral summer 1998/1999

INTRODUCTIONComparedwithotheroceansintheworld ,thereisrelativelyhigherlevelofnutrients (ni trate ,phosphate ,silicate)intheSouthernOcean .Butprimaryproductivitiesarelow ,andnewproductionisalsoonlyinthemiddlelevelthere .Itiscommonlyconsideredthatthelowerpro ductivitiesintheSouthernOceaniscausedbylowtemperature ,lowlight,lowstabilityofwa ter,scarcityoftraceelementsuchasironandgrazingbyzooplankton (Burkilletal.,1 995) ,etc.ThemostexistedstudiesconcentratedontheAtlanticSectoroftheSouthernO…     

南极普里兹湾浮游植物现存量与初级生产力粒级结构和新生产力研究

报道1998～1999年夏季在南极普里兹湾及其毗邻海域对细胞丰度、优势种类组成、生物量和初级生产力的粒级结构、新生产力及其环境制约机制的研究.结果表明,调查海区具有显著的空间区域化特征.普里兹湾及其毗邻陆架区浮游植物现存生物量和生产力均较高,大陆坡和深海区明显降低;营养盐浓度由于浮游植物的消耗则有相反的分布趋势.浮游植物生物量和生产力受水体的垂直稳定度、浮游动物摄食、水温和光照等环境条件的控制.粒度分级测定结果表明,对调查海区叶绿素a的贡献,小型浮游生物为52.2%,微型为29.4%,微微型为18.4%;对初级生产力的贡献,小型为52.4%,微型为28.7%,微微型为18.9%.研究海区的平均新生产力和f比分别为230.6mg/(m2·d)和0.43.     

西北太平洋137°E断面温度场和盐度场的时空特征

本文利用日本气象厅在137°E断面获得的水温和盐度长期观测资料,分析了该断面温度场和盐度场的时空特征.结果表明,137°E断面的温度场和盐度场都存在着明显的季节差异和年际变化.冬季,温度场变化的关键区位于3°～18°N的300m以浅海域,而盐度场变化的关键区则位于18°～34°N的300m以浅海域.夏季,温度场变化的关键区位于3°～16°N的300m以浅海域,而盐度场则有两个关键区,分别位于3°～18°N的200m以浅海域和24°～34°N的300m以浅海域.温度场的年际变化与ENSO循环相联系,而盐度场的年际变化则比较复杂.     

Phytoplankton pigment distribution in relation to silicic acid, iron and the physical structure across the Antarctic Polar Front, 170°W, during austral summer

In order to study the factors controlling the phytoplankton distribution across the Antarctic Polar Frontal Region (PFR), surface pigment samples were collected during austral summer (January/February 1998) near 170°W. Both the Polar Front (PF) and the Southern Antarctic Circumpolar Current Front (SACCF) were regions of enhanced accumulation of phytoplankton pigments. The mesoscale survey across the PF revealed two distinct phytoplankton assemblages on either side of the front. The phytoplankton community was dominated by diatoms south of the PF and by nanoflagellates (primarily by prymnesiophytes) to the north. Surprisingly, chlorophyll a concentrations did not correlate with mixed-layer depths. However, an increase of the dominance of diatoms over prymnesiophytes was observed with decreasing mixed-layer depths. Despite this relationship, we conclude that the average light availability in the mixed layer was not an important factor influencing the shift in phytoplankton composition across the PF. Although no correlation was found between the surface distribution of the major phytoplankton taxa and dissolved iron or silicic acid concentrations, the location of the strongest vertical gradient in silicic acid and iron concentration coincides with the maximum abundance of diatoms. We conclude that the difference in taxonomic composition is a result of increased silicic acid and iron flux to the upper mixed layer as a result of the increased vertical gradient of these key nutrients south of the front.     

Benthic remineralization and burial of biogenic SiO2, CaCO3, organic carbon, and detrital material in the Southern Ocean along a transect at 170° West

We investigated the composition, recycling, and mass accumulation rates of sediments along a transect in the Southern Ocean located from 66°S to 57°S at 170°W. This transect also corresponds to the location of a sediment trap mooring line. The sediments at the seven sites studied range from largely terrigenous material to nearly pure (>90%) biogenic silica. CaCO₃ is a minor but persistent component at most sites. Mass accumulation rates have been determined on the basis of excess ²³⁰Th in the sediments, i.e., ²³⁰Th-normalized accumulation rates. The influence of redistribution of sediments on the sea floor has been estimated from ¹⁴C analyses. The recycling of material delivered to the sediments has been characterized on the basis of pore water studies that make extensive use of both in situ sampling and shipboard extractions. The influence of the highly variable rates of input of particulate matter that characterize much of the Southern Ocean upon pore water gradients and fluxes across the sediment water interface has been considered.We find only poor correspondence between BSiO₂ burial fraction (=burial/particulate flux), a quantifiable measure of preservation efficiency, and BSiO₂ particulate rain along the transect. However, preservation does appear to be closely linked to a combination of sedimentation rate and particulate rain.The burial fraction of BSiO₂ is small relative to benthic rain (5–19%). Despite the small fraction buried, burial flux normalized to (sedimentation rate)^1/2 appears to provide a very consistent means of predicting benthic particulate rain over a large range of rain rates, including data from a number of different studies and environments. At sites with BSiO₂ rain 250 mmol m⁻² yr⁻¹ the average difference between predicted and observed rain is 25–30%. Such rain rates occur in many marine areas, particularly the Southern Ocean, with the result that this relationship potentially provides a means of estimating BSiO₂ benthic rain over prolonged periods in the past on the basis of readily measured sediment parameters.At the southern-most deep ocean station, the particulate flux was characterized by an extremely high C_org/CaCO₃ ratio (>10), but this high ratio does not appear to have a substantial influence on CaCO₃ burial. CaCO₃ is preserved in the sediments at this site despite a particulate flux with a 10-fold excess of C_org above that required for complete dissolution in the sediments. The unexpectedly high preservation of CaCO₃ is due largely to the very steep C_org oxidation rate profile at this site. As a result, a large fraction of the organic matter oxidized in the sediments does so in close proximity to the sediment–water interface where most of the metabolic CO₂ is neutralized by CO₃²⁻ from the overlying water, rather than by the dissolution of sedimentary CaCO₃.Diagenetic modeling indicates that at several of the stations, the remineralization fluxes of carbonate species across the sediment–water interface may not have been at steady state as a result of the highly pulsed nature of particulate rain in this environment. We estimate that at the time of our sampling it is possible that near-interface fluxes could have been a factor of 1.6–2 times the annual average.At every site on the transect, the burial fluxes of detrital material are substantially greater than the detrital particulate rain measured in the sediment traps, by as much as a factor of 40. Detrital burial is bimodal, being greatest at the southern and northern extremes of the transect. We postulate that the excess of burial over particulate rain in the south reflects the contribution of ice rafted debris at these high latitudes. Increases in the supply at the northern stations must have a different source. We believe that the excess at these stations is material eroded from the sea floor to the west, possibly on the Campbell Plateau, and advected by currents to the northern portion of the transect at depths below the shallow traps.     

Spatial and temporal distribution of cadmium and copper in water and zooplankton in the Bahía Blanca estuary,Argentina

Cadmium and copper in the dissolved and particulate phase and in zooplankton were determined in the Bahía Blanca estuary during six surveys from March to December 2005. Temperature, pH, salinity, dissolved oxygen, suspended particulate matter, particulate organic matter and chlorophyll-a were also considered. Dissolved Cd was below the detection limit (0.2 μg L⁻¹) for almost the entire study period whereas Cu concentrations (0.5–2.4 μg L⁻¹) indicated a continuous dissolved Cu input. Particulate Cd concentrations ranged from below the detection limit (<0.01) to 28.6 μg g⁻¹ d.w. while particulate Cu ranged from below the detection limit (<0.04) to 53.5 μg g⁻¹ d.w. Cd in mesozooplankton ranged from below the detection limit (<0.01) to 37.4 μg g⁻¹ d.w. Some of the Cd levels were higher than those reported for other aquatic ecosystems. Cu in the mesozooplankton ranged from 1.3 to 89.3 μg g⁻¹ d.w., values which were within the reported values or higher than other studies. The log of the partition coefficients (log (K_d)) of Cd was 0.04, while log (K_d) for Cu ranged from −0.39 to 2.79. These values were lower than both those calculated for other estuaries and the typical coefficients for marine environments. The log of the bioconcentration factor (log BCF) of Cd was 1.78, indicating that Cd concentration was higher in the zooplankton than in the dissolved phase. Log BCF of Cu ranged from 1.15 to 3. The logs of the biomagnification factors (log BMF) of Cd were low, with a range between −3.45 and 2.21 and those for Cu ranged from −0.1 to 3.35. Positive values indicate biomagnification while negative values indicate biodiminution. In general, no significant dissolved Cd concentration appeared to be present in the Bahía Blanca estuary and Cu values did not indicate a critical environmental status. The particulate phase seemed to be the major carrier for Cd and Cu and TPCu values were within the normal values for an anthropogenically stressed estuary but not for a strongly polluted system. This fraction was the most important metal source for the mesozooplankton. Moreover, the highest metal concentrations were in the mesozooplankton since most of the bioconcentration and biomagnification factors were positive, especially for Cu.     

Origin of iron and aluminium in large particles (> 53 µm) in the Crozet region, Southern Ocean

Natural iron fertilization processes are occurring around the Crozet Islands (46°26′S–52°18′E), thus relieving the water masses from the normally encountered High Nutrients Low Chlorophyll (HNLC) conditions of the Southern Ocean. During austral summers 2004/2005 and 2005/2006, iron and aluminium concentrations were investigated in large particles (> 53 µm) collected from just below the mixed layer at stations under the influence of island inputs, and also in adjacent HNLC waters. These large particles are anticipated to sink out of the mixed layer, and to reflect the net effects of input and cycling of these elements in the overlying mixed layer. Labile and refractory fractions were determined by a two-stage leaching technique. Data showed that water masses downstream of the islands were enriched in total iron and aluminium (0.25–2.68 nmol L^− 1 and 0.34–3.28 nmol L^− 1 respectively), relative to the southern HNLC control sites (0.15–0.29 nmol L^− 1 for Fe and 0.12–0.29 nmol L^− 1 for Al), with only a small fraction (typically < 1%) being acid leachable in both environments. Particulate iron predominantly derived from the island system represents a significant fraction of the total water column iron inventory and may complement dissolved Fe inputs that help support the high summer productivity around the Crozet islands.