Variability of chlorophyll and primary production in the Eastern North Atlantic Subtropical Gyre: potential factors affecting phytoplankton activity

Size-fractionated chlorophyll-a and carbon incorporation rates were determined on a series of 13 cruises carried out from 1992 to 2001with the aim of investigating the patterns and causes of variability in phytoplankton chlorophyll and production in the Eastern North Atlantic Subtropical Gyral Province (NASE). Averaged (±SE) integrated chlorophyll-a concentration and primary production rate were 17±1 mg m⁻² and 253±22 mg C m⁻² d⁻¹. Small-sized cells (<2 μm) formed the bulk of phytoplankton biomass (71%) and accounted for 54% of total primary production. A clear latitudinal gradient in these variables was not detected. By contrast, large seasonal variability was detected in terms of primary production, although integrated phytoplankton biomass, as estimated from chlorophyll-a concentration, remained rather constant and did not display significant changes with time. Variability in primary production (PP) was related mainly to variability in surface temperature and surface chlorophyll-a concentration. The control exerted by surface temperature was related to nutrient availability. By contrary, euphotic-zone depth, depth of maximum concentration of chlorophyll-a and integrated chlorophyll-a did not contribute significantly to the high variability in primary production observed in this oligotrophic region.     

Depth habitats and seasonal distributions of recent planktic foraminifers in the Canary Islands region (29°N) based on oxygen isotopes

Seasonal depth stratified plankton tows, sediment traps and core tops taken from the same stations along a transect at 29°N off NW Africa are used to describe the seasonal succession, the depth habitats and the oxygen isotope ratios (δ¹⁸O_shell) of five planktic foraminiferal species. Both the δ¹⁸O_shell and shell concentration profiles show variations in seasonal depth habitats of individual species. None of the species maintain a specific habitat depth exclusively within the surface mixed layer (SML), within the thermocline, or beneath the thermocline. Globigerinoides ruber (white) and (pink) occur with moderate abundance throughout the year along the transect, with highest abundances in the winter and summer/fall season, respectively. The average δ¹⁸O_shell of G. ruber (w) from surface sediments is similar to the δ¹⁸O_shell values measured from the sediment-trap samples during winter. However, the δ¹⁸O_shell of G. ruber (w) underestimates sea surface temperature (SST) by 2 °C in winter and by 4 °C during summer/fall indicating an extension of the calcification/depth habitat into colder thermocline waters. Globigerinoides ruber (p) continues to calcify below the SML as well, particularly in summer/fall when the chlorophyll maximum is found within the thermocline. Its vertical distribution results in δ¹⁸O_shell values that underestimate SST by 2 °C. Shell fluxes of Globigerina bulloides are highest in summer/fall, where it lives and calcifies in association with the deep chlorophyll maximum found within the thermocline. Pulleniatina obliquiloculata and Globorotalia truncatulinoides, dwelling and calcifying a part of their lives in the winter SML, record winter thermocline (～180 m) and deep surface water (～350 m) temperatures, respectively. Our observations define the seasonal and vertical distribution of multiple species of foraminifera and the acquisition of their δ¹⁸O_shell.     

Latitudinal distribution of microbial plankton abundance,production, and respiration in the Equatorial Atlantic in autumn 2000

Phytoplankton and bacterial abundance, size-fractionated phytoplankton chlorophyll-a (Chl-a) and production together with bacterial production, microbial oxygen production and respiration rates were measured along a transect that crossed the Equatorial Atlantic Ocean (10°N–10°S) in September 2000, as part of the Atlantic Meridional Transect 11 (AMT 11) cruise. From 2°N to 5°S, the equatorial divergence resulted in a shallowing of the pycnocline and the presence of relatively high nitrate (>1 μM) concentrations in surface waters. In contrast, a typical tropical structure (TTS) was found near the ends of the transect. Photic zone integrated ¹⁴C primary production ranged from ∼200 mg C m⁻² d⁻¹ in the TTS region to ∼1300 mg C m⁻² d⁻¹ in the equatorial divergence area. In spite of the relatively high primary production rates measured in the equatorial upwelling region, only a moderate rise in phytoplankton biomass was observed as compared to nearby nutrient-depleted areas (22 vs. 18 mg Chl-a m⁻², respectively). Picophytoplankton were the main contributors (>60%) to both Chl-a biomass and primary production throughout the region. The equatorial upwelling did not alter the phytoplankton size structure typically found in the tropical open ocean, which suggests a strong top-down control of primary producers by zooplankton. However, the impact of nutrient supply on net microbial community metabolism, integrated over the euphotic layer, was evidenced by an average net microbial community production within the equatorial divergence (1130 mg C m⁻² d⁻¹) three-fold larger than net production measured in the TTS region (370 mg C m⁻² d⁻¹). The entire region under study showed net autotrophic community metabolism, since respiration accounted on average for 51% of gross primary production integrated over the euphotic layer.     

Distribution of bacterial abundance and cell-specific nucleic acid content in the Northeast Pacific Ocean

We tested the idea that bacterial cells with high nucleic acid content (HNA cells) are the active component of marine bacterioplankton assemblages, while bacteria with low nucleic acid content (LNA cells) are inactive, with a large data set (>1700 discrete samples) based on flow cytometric analysis of bacterioplankton in the Northeast Pacific Ocean off the coast of Oregon and northern California, USA. Samples were collected in the upper 150 m of the water column from the coast to 250 km offshore during 14 cruises from March 2001 to September 2003. During this period, a wide range of trophic states was encountered, from dense diatom blooms (chlorophyll-a concentrations up to 43 μg l⁻¹) at shelf stations during upwelling season (March–September) to lower chlorophyll-a concentrations (0.1–5 μg l⁻¹) during winter (November–February) and at basin stations (>1700 m depth). We found only weakly positive relations of log total bacterial abundance to log chlorophyll-a concentration (as a proxy for availability of organic substrate), and of HNA bacteria as a fraction of total bacteria to log chlorophyll-a. Abundance of HNA and LNA bacteria co-varied positively in all regions, although HNA bacteria were more responsive to high phytoplankton biomass in shelf waters than in slope and basin waters. Since LNA cell abundance in general showed responses similar to those of HNA cell abundance to changes in phytoplankton biomass, our data do not support the hypothesis that HNA cells are the sole active component of marine bacterioplankton.     

A quantitative analysis of sources for summertime phytoplankton variability over 18 years in the South Shetland Islands (Antarctica) region

Eighteen years of summertime hydrographic and chlorophyll-a (Chl-a) data (～2700 stations) from the South Shetland Islands (Antarctica) region show that a “bell-shaped” (unimodal) distribution of phytoplankton biomass results annually when plotted against the inshore to offshore gradient in surface salinity. The maximum for this unimodal Chl-a distribution corresponds with a shallow upper mixed layer (UML) in iron-rich waters that occurs at salinities ～34. Methods of gradient analysis are used to distinguish sources of variability for bloom development among years. The control of phytoplankton biomass is resolved across the salinity gradient that separates the co-limiting conditions of deep UML depths and low-iron concentrations as opposing end-members. Chlorophyll-fluorescence yield data (a proxy for Fe-stress) showed that at salinities ～34, phytoplankton biomass was unlikely to be limited by Fe. Instead, blooming at salinities ～34 (1.3±1 mg Chl-a m^?3) co-varied with shallow UML depths (41±19 m) that occurred as a function of higher UML temperature (1.5±0.5 °C) among years, and is evidence that atmospheric climate variability impacts summertime phytoplankton biomass and production in this Southern Ocean seascape.     

Modelling phytoplankton deposition to Chesapeake Bay sediments during winter–spring: interannual variability in relation to river flow

The often-rapid deposition of phytoplankton to sediments at the end of the spring phytoplankton bloom is an important component of benthic–pelagic coupling in temperate and high latitude estuaries and other aquatic systems. However, quantifying the flux is difficult, particularly in spatially heterogeneous environments. Surficial sediment chlorophyll-a, which can be measured quickly at many locations, has been used effectively by previous studies as an indicator of phytoplankton deposition to estuarine sediments. In this study, surficial sediment chlorophyll-a was quantified in late spring at 20–50 locations throughout Chesapeake Bay for 8 years (1993–2000). A model was developed to estimate chlorophyll-a deposition to sediments using these measurements, while accounting for chlorophyll-a degradation during the time between deposition and sampling. Carbon flux was derived from these estimates via C:chl-a = 75.Bay-wide, the accumulation of chlorophyll-a on sediments by late spring averaged 171 mg m⁻², from which the chlorophyll-a and carbon sinking fluxes, respectively, were estimated to be 353 mg m⁻² and 26.5 gC m⁻². These deposition estimates were ∼50% of estimates based on a sediment trap study in the mid-Bay. During 1993–2000, the highest average chlorophyll-a flux was in the mid-Bay (248 mg m⁻²), while the lowest was in the lower Bay (191 mg m⁻²). Winter–spring average river flow was positively correlated with phytoplankton biomass in the lower Bay water column, while phytoplankton biomass in that same region of the Bay was correlated with increased chlorophyll-a deposition to sediments. Responses in other regions of the Bay were less clear and suggested that the concept that nutrient enrichment in high flow years leads to greater phytoplankton deposition to sediments may be an oversimplification. A comparison of the carbon flux associated with the deposition of the spring bloom with annual benthic carbon budgets indicated that the spring bloom did not contribute a disproportionately large fraction of annual carbon inputs to Chesapeake Bay sediments. Regional patterns in chlorophyll-a deposition did not correspond with the strong regional patterns that have been found for plankton net community metabolism during spring.     

On-line determination of silver in natural waters by inductively-coupled plasma mass spectrometry: Influence of organic matter

We investigated interference effects on the analysis of silver in estuarine and oceanic waters using on-line high resolution inductively coupled plasma mass spectrometry (ICP-MS). A mini-column packed with a strong anion exchange resin (Dowex 1-X8) was used in a flow-injection system to separate and concentrate silver from the saline samples prior to on-line determination by ICP-MS. A series of analyses showed the concentrations of silver measured in San Francisco Bay estuary and the North Pacific that had been acidified (pH < 2) and stored for periods of 1–2 years were 10–70% lower than those measured in aliquots of those samples after ultraviolet (UV) irradiation. Additional silver released after UV irradiation of the estuarine waters, but not the ocean waters, was positively correlated (r = 0.77, simple linear correlation) with chlorophyll-a concentrations, but not with dissolved organic carbon (DOC) concentrations. Spatial distributions of chlorophyll-a and UV-released silver also exhibited similar patterns along a salinity gradient in the San Francisco Bay estuary, suggesting an in situ biogenic source of the interferent for the silver measurements.     

Abundance and size distribution of transparent exopolymer particles (TEP) in a coccolithophorid bloom in the northern Bay of Biscay

The distribution of transparent exopolymer particles (TEP) was investigated during a coccolithophorid bloom in the northern Bay of Biscay (North Atlantic Ocean) in early June 2006. MODIS chlorophyll-a (Chl-a) and reflectance images before and during the cruise were used to localize areas of important biological activity and high reflectance (HR). TEP profiles along the continental margin, determined using microscopic (TEP_micro) and colorimetric (TEP_color) methods, showed abundant (6.1×10⁶–4.4×10⁷ L^?1) and relatively small (0.5–20 μm) particles, leading to a low total volume fraction (0.05–2.2 ppm) of TEP_micro and similar vertical profiles of TEP_color. Estimates of carbon content in TEP (TEP-C) derived from the microscopic approach yielded surface concentration of 1.50 μmol C L^?1. The contribution of TEP-C to particulate organic carbon (POC) was estimated to be 12% (molar C ratio) during this survey. Our results suggest that TEP formation is a probable first step to rapid and efficient export of C during declining coccolithophorid blooms.     

Factors influencing particulate lipid production in the East Atlantic Ocean

Extensive analyses of particulate lipids and lipid classes were conducted to gain insight into lipid production and related factors along the biogeochemical provinces of the Eastern Atlantic Ocean. Data are supported by particulate organic carbon (POC), chlorophyll a (Chl a), phaeopigments, Chl a concentrations and carbon content of eukaryotic micro-, nano- and picophytoplankton, including cell abundances for the latter two and for cyanobacteria and prokaryotic heterotrophs. We focused on the productive ocean surface (2 m depth and deep Chl a maximum (DCM)). Samples from the deep ocean provided information about the relative reactivity and preservation potential of particular lipid classes. Surface and DCM particulate lipid concentrations (3.5–29.4 μg L⁻¹) were higher than in samples from deep waters (3.2–9.3 μg L⁻¹) where an increased contribution to the POC pool was observed. The highest lipid concentrations were measured in high latitude temperate waters and in the North Atlantic Tropical Gyral Province (13–25°N). Factors responsible for the enhanced lipid synthesis in the eastern Atlantic appeared to be phytoplankton size (micro, nano, pico) and the low nutrient status with microphytoplankton having the most expressed influence in the surface and eukaryotic nano- and picophytoplankton in the DCM layer. Higher lipid to Chl a ratios suggest enhanced lipid biosynthesis in the nutrient poorer regions. The various lipid classes pointed to possible mechanisms of phytoplankton adaptation to the nutritional conditions. Thus, it is likely that adaptation comprises the replacement of membrane phospholipids by non-phosphorus containing glycolipids under low phosphorus conditions. The qualitative and quantitative lipid compositions revealed that phospholipids were the most degradable lipids, and their occurrence decreased with increasing depth. In contrast, wax esters, possibly originating from zooplankton, survived downward transport probably due to the fast sinking rate of particles (fecal pellets). The important contribution of glycolipids in deep waters reflected their relatively stable nature and degradation resistance. A lipid-based proxy for the lipid degradative state (Lipolysis Index) suggests that many lipid classes were quite resistant to degradation even in the deep ocean.     

Seasonal variation of pteropods from the Western Arabian Sea sediment trap

Sediment trap samples collected from the Western Arabian Sea yielded a rich assemblage of intact and non-living (opaque white) pteropod tests from a water depth of 919 m during January to September 1993. Nine species of pteropods were recorded, all (except one) displaying distinct seasonality in abundance, suggesting their response to changing hydrographical conditions influenced by the summer/winter monsoon cycle. Pteropod fluxes increased during the April–May peak of the intermonsoon, and reached maximum levels in the late phase of the southwest summer monsoon, probably due to the shallowing of the mixed layer depth. This shallowing, coupled with enhanced nutrient availability, provides ideal conditions for pteropod growth, also reflected in corresponding fluctuations in the flux of the foraminifer Globigerina bulloides. Pteropod/planktic foraminifer ratios displayed marked seasonal variations, the values increasing during the warmer months of April and May when planktic foraminiferal fluxes declined. The variation in fluxes of calcium carbonate, organic carbon and biogenic opal show positive correlations with fluxes of pteropods and planktic foraminifers. Calcium carbonate was the main contributor to the total particulate flux, especially during the SW monsoon. In the study area, pteropod flux variations are similar to the other flux patterns, indicating that they, too could be used as a potential tool for palaeoclimatic reconstruction of the recent past.     

Dissolved organic carbon and apparent oxygen utilization in the Atlantic Ocean

Dissolved organic carbon (DOC) distributions along two Atlantic Meridional Transects conducted in 2005 in the region between 47°N and 34°S showed clear latitudinal patterns. The DOC concentrations in the epipelagic zone (0–100 m) were the highest (70–90 µM) in tropical and subtropical waters with stable mixed layers, and lowest (50–55 µM) at the poleward extremities of the transects due to deep convective mixing supplying low DOC waters to the surface. A decrease in DOC occurred with depth, and lowest DOC concentrations (41–45 µM) in the 100–300 m depth range were observed in the equatorial region due to upwelling of low DOC waters. A strong relationship between DOC and AOU was observed in the σ–t 26–26.5 isopycnal layer which underlies the euphotic zone and outcrops at the poleward extremities of the North and South Atlantic Subtropical Gyres (NASG and SASG) in the region ventilating the thermocline waters. Our observations reveal significant north–south variability in the DOC–AOU relationship. The gradient of the relationship suggests that 52% of the AOU in the σ–t 26–26.5 density range was driven by DOC degradation in the NASG and 36% in the SASG, with the remainder due to the remineralisation of sinking particulate material. We assess possible causes for the greater contribution of DOC remineralisation in the NASG compared to the SASG.     

Behaviors of dissolved and particulate Co,Ni, Cu,Zn, Cd and Pb during a mesoscale Fe-enrichment experiment (SEEDS II) in the western North Pacific

During mesoscale Fe enrichment (SEEDS II) in the western North Pacific ocean, we investigated dissolved and particulate Co, Ni, Cu, Zn, Cd and Pb in seawater from both field observation and shipboard bottle incubation of a natural phytoplankton assemblage with Fe addition. Before the Fe enrichment, strong correlations between dissolved trace metals (Ni, Zn and Cd) and PO₄³⁻, and between particulate trace metals (Ni, Zn and Cd) and chlorophyll-a were obtained, suggesting that biogeochemical cycles mainly control the distributions of Ni, Zn and Cd in the study area. Average concentrations of dissolved Co, Ni, Cu, Zn, Cd and Pb in the surface mixed layer (0–20 m) were 70 pM, 4.9, 2.1, 1.6, 0.48 nM and 52 pM, respectively, and those for the particulate species were 1.7 pM, 0.052, 0.094, 0.46, 0.037 nM and 5.2 pM, respectively. After Fe enrichment, chlorophyll-a increased 3 fold (up to 3 μg L⁻¹) during developing phases of the bloom (<12 days). Mesozooplankton biomass also increased. Particulate Co, Ni, Cu and Cd inside the patch hinted at an increase in the concentrations, but there were no analytically significant differences between concentrations inside and outside the patch. The bottle incubation with Fe addition (1 nM) showed an increase in chlorophyll-a (8.9 μg L⁻¹) and raised the particulate fraction up to 3–45% for all the metals, accompanying changes in Si/P, Zn/P and Cd/P. These results suggest that Fe addition lead to changes in biogeochemical cycling of trace metals. The comparison between the mesoscale Fe enrichment and the bottle incubation experiment suggests that although Fe was a limiting factor for the growth of phytoplankton, the enhanced biomass of mesozooplankton also limited the growth of phytoplankton and the transformation of trace metal speciation during the mesoscale Fe enrichment. Sediment trap data and the elemental ratios taken up by phytoplankton suggest that export loss was another reason that no detectable change in the concentrations of particulate trace metals was observed during the mesoscale Fe enrichment.     

Basin-scale variability of phytoplankton biomass,production and growth in the Atlantic Ocean

The latitudinal distributions of phytoplankton biomass, composition and production in the Atlantic Ocean were determined along a 10,000-km transect from 50°N to 50°S in October 1995, May 1996 and October 1996. Highest levels of euphotic layer-integrated chlorophyll a (Chl a) concentration (75–125 mg Chl m⁻²) were found in North Atlantic temperate waters and in the upwelling region off NW Africa, whereas typical Chl a concentrations in oligotrophic waters ranged from 20 to 40 mg Chl m⁻². The estimated concentration of surface phytoplankton carbon (C) biomass was 5–15 mg C m⁻² in the oligotrophic regions and increased over 40 mg C m⁻² in richer areas. The deep chlorophyll maximum did not seem to constitute a biomass or productivity maximum, but resulted mainly from an increase in the Chl a to C ratio and represented a relatively small contribution to total integrated productivity. Primary production rates varied from 50 mg C m⁻² d⁻¹ at the central gyres to 500–1000 mg C m⁻² d⁻¹ in upwelling and higher latitude regions, where faster growth rates (μ) of phytoplankton (>0.5 d⁻¹) were also measured. In oligotrophic waters, microalgal growth was consistently slow [surface μ averaged 0.21±0.02 d⁻¹ (mean±SE)], representing <20% of maximum expected growth. These results argue against the view that the subtropical gyres are characterized by high phytoplankton turnover rates. The latitudinal variations in μ were inversely correlated to the changes in the depth of the nitracline and positively correlated to those of the integrated nitrate concentration, supporting the case for the role of nutrients in controlling the large-scale distribution of phytoplankton growth rates. We observed a large degree of temporal variability in the phytoplankton dynamics in the oligotrophic regions: productivity and growth rates varied in excess of 8-fold, whereas microalgal biomass remained relatively constant. The observed spatial and temporal variability in the biomass specific rate of photosynthesis is at least three times larger than currently assumed in most satellite-based models of global productivity.     

Vertical distribution of phytoplankton biomass,production and growth in the Atlantic subtropical gyres

Ninety-four stations were sampled in the Atlantic subtropical gyres during 10 cruises carried out between 1995 and 2001, mainly in boreal spring and autumn. Chlorophyll a (Chl-a) and primary production were measured during all cruises, and phytoplankton biomass was estimated in part of them. Picoplankton (<2 μm) represented >60% of total Chl-a concentration measured at the surface, and their contribution to this variable increased with depth. Phytoplankton carbon concentrations were higher in the upper metres of the water column, whereas Chl-a showed a deep maximum (DCM). At each station, the water column was divided into the upper mixed layer (ML) and the DCM layer (DCML). The boundary between the two layers was calculated as the depth where Chl-a concentration was 50% of the maximum Chl-a concentration. On average DCML extends from 67 to 126 m depth. Carbon to Chl-a (C:Chl-a) ratios were used to estimate phytoplankton carbon content from Chl-a in order to obtain a large phytoplankton carbon dataset. Total C:Chl-a ratios averaged (±s.e.) 103±7 (n=22) in the ML and 24±4 (n=12) in the DCML and were higher in larger cells than in picoplankton. Using these ratios and primary production measurements, we derived mean specific growth rates of 0.17±0.01 d⁻¹ (n=173) in the ML and 0.20±0.01 d⁻¹ (n=165) in the DCML although the differences were not significant (t-test, p>0.05). Our results suggest a moderate contribution of the DCML (43%) to both phytoplankton biomass and primary production in the Atlantic subtropical gyres.     

Enhancement of particulate organic carbon export flux induced by atmospheric forcing in the subtropical oligotrophic northwest Pacific Ocean

The effects of extreme atmospheric forcing on the export flux of particulate organic carbon (POC) in the warm oligotrophic nitrogen-limited northwest Pacific Ocean were examined in 2007 during the spring Asian dust storm period. Several strong northeast monsoon events (maximum sustained wind speeds approaching 16.7 m s^? 1, and gusts up to 19.0 m s^? 1) accompanied by dust storms occurred during a 1-month period. The cold stormy events decreased surface water temperature and induced strong wind-driven vertical mixing of the water column, resulting in nutrient entrainment into the mixed layer from subsurface waters. As a result, the export flux of POC ranged from 49 to 98 (average value = 71 ± 16) mg m^? 2 day^? 1, approximately 2–3 times greater than average values in other seasons. As dry and wet deposition of nitrogen attributable to Asian dust storm events does not account for the associated increases in POC stocks in this N-limited oligotrophic oceanic region, the enhancement of POC flux must have been caused by nutrient entrainment from subsurface waters because of the high winds accompanying the dust storm events.     

New and regenerated production in the Almeria-Oran front area,eastern Alboran Sea

Uptake and regeneration of nitrogen in the Almeria-Oran frontal zone (SW Mediterranean) and adjacent (Atlantic and Mediterranean) systems were studied during the Almofront I cruise (JGOFS-France). The frontal zone was characterized by an upsloping of nitracline from about 50 m in the adjacent systems to 25–30 m within. Along with nitrate, ammonium, chlorophyll a and particulate organic nitrogen also were at higher concentrations in the frontal zone than in the adjacent waters.The nitrate uptake rates were significantly higher in the frontal zone (up to 6.4 nmol l⁻¹ h⁻¹) than in the Atlantic and Mediterranean waters (generally <1 nmol l⁻¹ h⁻¹) indicating a significant increase of new production at the front. This increase was related to the upsloping of the nitracline as shown by the significant correlation (p<0.05) between new production and depth of the nitracline. The new production in the Almeria-Oran was much lower than those recorded in other oceanic and coastal fronts. This could be related to the fact that the nitracline did not rise up to the surface and the high concentrations of nitrate were confined to deeper layers where the ambient light intensity was less. Nitrate uptake in the frontal zone was significantly higher, by 1.7–5.8 times (average 4.2), than the calculated diffusive flux of nitrate, suggesting that vertical advection may be an important source of nitrate. New production rates at the front were also significantly higher (3–9 times, average 5.8) than the PON flux to 100 m depth estimated by sediments traps (Journal of Marine Systems 5, 377–389), suggesting a strong decoupling between surface production and downward flux of POM in the frontal zone.The north–south gradient observed with different parameters indicates the presence of a transfrontal secondary circulation. This distribution also suggests that the primary production in the front is initially nitrate-based, with a diatom-herbivore food chain, whereas regenerated production, associated with an intense recycling of organic matter, later becomes progressively important in time and space.     

Distributions and fluxes of methyl chloride and methyl bromide in the East China Sea and the Southern Yellow Sea in autumn

We determined the distributions and fluxes of methyl chloride and methyl bromide in the East China Sea (ECS) and the Southern Yellow Sea (SYS) in November 2007. Methyl chloride and methyl bromide concentrations in the surface waters ranged from 47.1 to 163 pmol L^?1 and from 0.70 to 9.82 pmol L^? 1, with average values of 87.6 and 2.97 pmol L^? 1, respectively. The distributions of the two methyl halides were clearly influenced by the Yangtze (Changjiang) River effluent and Kuroshio water, with high concentrations appearing in the coastal zone and low values occurring in the open waters. A positive linear correlation was observed between methyl chloride and methyl bromide concentration anomalies in the surface waters, suggesting that they may share some origins in this coastal area. However, no correlation was found between the two methyl halide concentration anomalies and chlorophyll a in the surface waters. The vertical profiles of the two methyl halides were characterized by the maxima in the upper mixed layer. Both gases were generally supersaturated in the surface seawater, with mean sea-to-air fluxes of methyl chloride and methyl bromide of 391 and 20.0 nmol m^?2 d^? 1, respectively.     

Particulate organic carbon in the global ocean derived from SeaWiFS ocean color

Satellite remote sensing offers new means of quantifying particulate organic carbon, POC, concentration over large oceanic areas. From SeaWiFS ocean color, we derived 10-year data of POC concentration in the surface waters of the global ocean. The 10-year time series of the global and basin scale average surface POC concentration do not display any significant long-term trends. The annual mean surface POC concentration and its seasonal amplitude are highest in the North Atlantic and lowest in the South Pacific, when compared to other ocean basins. POC anomalies in the North Atlantic, North Pacific, and global concentrations seem to be inversely correlated with El Niño index, but longer time series are needed to confirm this relationship. Quantitative estimates of POC reservoir in the oceanic surface layer depend on the choice of what should represent this layer. Global average POC biomass is 1.34 g m^?2 if integrated over one optical depth, 3.62 g m^?2 if integrated over mixed layer depth, and up to 6.41 g m^?2 if integrated over 200-m layer depth (when assumed POC concentration below MLD is 20 mg m^?3). The global estimate of total POC reservoir in the surface 200-m layer of the ocean is 228.61×10¹³ g. We expect that future estimates of POC reservoir may be even larger, when more precise calculations account for deep-water organic-matter maxima in oligotrophic regions, and POC biomass located just below the seasonal mixed layer in spring and summer in the temperate regions.     

Original oxygen isotopic composition of planktic foraminifers preserved in diagenetically altered Pleistocene shallow-marine carbonates

The original stable isotopic composition of low-Mg calcitic planktic foraminifer tests is preserved in Pleistocene shallow-marine carbonates (in the Ryukyu Group; Okinawa, Japan) that have been altered by meteoric diagenesis. Whole-rock analyses indicate depleted isotopic values for both δ¹³C (−1.9 to −5.4‰) and δ¹⁸O (−2.9 to −5.2‰), as well as carbonate mineralogy exclusively composed of low-Mg calcite. However, analysis of carefully-extracted planktic foraminifer tests (Globigerinoides sacculifer) that were separated from these whole-rock samples yield heavier δ¹³C values (−0.4 to 1.9‰) and δ¹⁸O values (−3.2 to −1.0‰). The foraminiferal values themselves and comparison of values of various components suggest that the low-Mg calcite tests preserve the original stable isotopic values. Subsequently, the downcore δ¹⁸O change of planktic foraminifers recorded in the Ryukyu Group results from middle Pleistocene glacial–interglacial change. By comparison, isotopic measurements based on whole-rock samples can be obtained diagenetic environmental signals, but misleading with regard to paleoclimatic inferences.     

Algal class abundances,estimated from chlorophyll and carotenoid pigments,in the western Equatorial Pacific under El Niño and non-El Niño conditions

Phytoplankton samples were collected from the equatorial Pacific (10°S to 10°N along 155°E) in June 1992 as part of the Australian contribution to the JGOFS program. Chlorophyll and carotenoid pigments were measured by HPLC, and a PC-based computer program (CHEMTAX) was used to estimate the contribution of 9 algal classes to the total chlorophyll a concentration in 9 separate depth bands at each location. This cruise occurred in the middle of the prolonged 1991/1993 El Niño, and the results are compared with similar data from a cruise in October 1990 which occurred before this El Niño but after the 1988/1989 La Niña.Changes in the pigment : chlorophyll a ratios appeared consistent across algal classes and, apart from some minor exceptions, consistent between cruises. Pigments involved in light-harvesting generally increased relative to chlorophyll a with increasing depth, whereas the ratio for photoprotective pigments (e.g. diadinoxanthin) usually decreased with depth. The zeaxanthin concentration per cell for cyanobacteria decreased with depth in the surface 75 m during 1992 as would be expected for a photoprotective pigment.Based on their contribution to the total chlorophyll a concentration, haptophytes, prochlorophytes, cyanobacteria (Synechococcus) and chlorophytes were the dominant algal classes in 1992. The chlorophyte contribution to chlorophyll a in 1992 (14.8%) was almost double that in 1990 (7.8%). This increase was largely at the expense of the cyanobacteria and haptophytes, which both decreased significantly. The increase in chlorophytes in 1992 was particularly noticeable in the surface waters south of the equator at about 4°S, where there was evidence of upwelling.