Surface Particulate Organic Matter Research Articles

Trophic niche of a neustonic copepod community sustained by local production in high- and low-salinity summer water masses in the northeastern East China Sea

We investigated the trophic dynamics between neustonic copepod communities and particulate organic matter (POM) sourced from contrasting water masses, i.e., high- and low-salinity areas, within the northeastern East China Sea. The sampling of neustonic copepod communities occurred three times in the summer (June, August, and September) of 2021, and considered the influx of the Yangtze River Diluted Water (YRDW) and the extension of the Tsushima Warm Current (TWC). To examine the relationship between the neustonic copepods and surface POM, we employed stable isotope techniques. Surprisingly, the neustonic copepod community exhibited a reluctance to feed on surface POM. The neustonic copepod community in the YRDW-dominated area in August showed higher δ13C values than those in the TWC-dominated area. The trophic groups within the neustonic copepod population appeared to consume selectively depending on the individual preferred prey sizes and composition. Using the POM from the water masses that affected the food sources consumed by neustonic copepods, we found a strong dependence on prey items originating from the TWC. This result suggests that the marine neustonic copepod community does not rely significantly on food sources derived from riverine freshwater.

Macroalgal input into the coastal food web along a gradient of seasonal sea ice cover along the Western Antarctic Peninsula

Coastal food webs that are supported by multiple primary producer sources are considered to be more stable against perturbations. Here, we investigated how declining macroalgal abundance and diversity might influence coastal food web structure along an annual sea ice cover gradient along the Western Antarctic Peninsula (WAP). The most common benthic invertebrate consumers, macroalgae, and surface particulate organic matter were collected at 15 stations along the WAP. Stable carbon and nitrogen isotope values of primary producers changed negligibly in relation to the sea ice cover gradient, while isotope values of most invertebrate feeding groups increased with higher sea ice cover, although at low explanatory power. Food web length became shorter and consumer trophic niche width smaller in regions with higher sea ice cover. Changes in food web structure were mostly associated with shifts in trophic position of lower trophic levels. Food web structure in higher ice-covered regions resembled that of more generalist feeders with a loss of specialist species, concurrent with an increased reliance on a more reworked detrital food source. These results suggest that a number of benthic invertebrates are able to adjust to differences in basal energy sources. Conversely, these food webs dominated by generalist feeders are likely less efficient in energy transfer, which can create less-stable systems with lower adaptive capacity to disturbance. The predicted sea ice loss along the WAP may ultimately lead to a longer food web with higher macroalgal abundance, more specialist species, and wider consumer trophic niches in the currently more ice-covered regions.

Isoscape Models of the Southern Ocean: Predicting Spatial and Temporal Variability in Carbon and Nitrogen Isotope Compositions of Particulate Organic Matter

AbstractPolar marine ecosystems are particularly vulnerable to the effects of climate change. Warming temperatures, freshening seawater, and disruption to sea‐ice formation potentially all have cascading effects on food webs. New approaches are needed to better understand spatiotemporal interactions among biogeochemical processes at the base of Southern Ocean food webs. In marine systems, isoscapes (models of the spatial variation in the stable isotopic composition) of carbon and nitrogen have proven useful in identifying spatial variation in a range of biogeochemical processes, such as nutrient utilization by phytoplankton. Isoscapes provide a baseline for interpreting stable isotope compositions of higher trophic level animals in movement, migration, and diet research. Here, we produce carbon and nitrogen isoscapes across the entire Southern Ocean (>40°S) using surface particulate organic matter isotope data, collected over the past 50 years. We use Integrated Nested Laplace Approximation‐based approaches to predict mean annual isoscapes and four seasonal isoscapes using a suite of environmental data as predictor variables. Clear spatial gradients in δ13C and δ15N values were predicted across the Southern Ocean, consistent with previous statistical and mechanistic views of isotopic variability in this region. We identify strong seasonal variability in both carbon and nitrogen isoscapes, with key implications for the use of static or annual average isoscape baselines in animal studies attempting to document seasonal migratory or foraging behaviors.

Linking a Latitudinal Gradient in Ocean Hydrography and Elemental Stoichiometry in the Eastern Pacific Ocean

AbstractA past global synthesis of marine particulate organic matter (POM) suggested latitudinal variation in the ratio of surface carbon (C): nitrogen (N): phosphorus (P). However, this synthesis relied on compiled datasets that may have biased the observed pattern. To demonstrate latitudinal shifts in surface C:N:P, we combined hydrographic and POM observations from 28°N to 69°S in the eastern Pacific Ocean (GO‐SHIP line P18). Both POM concentrations and ratios displayed distinct biome‐associated changes. Surface POM concentrations were relatively low in the North Pacific subtropical gyre, increased through the Equatorial Pacific, were lowest in the South Pacific subtropical gyre, and increased through the Southern Ocean. Stoichiometric elemental ratios were systematically above Redfield proportions in warmer regions. However, C:P and N:P gradually decreased across the Southern Ocean despite an abundance of macro‐nutrients. Here, a size‐fraction analysis of POM linked increases in the proportion of large plankton to declining ratios. Subsurface N* values support the hypothesis that accumulated remineralization products of low C:P and N:P exported POM helps maintain the Redfield Ratio of deep nutrients. We finally evaluated stoichiometric models against observations to assess predictive accuracy. We attributed the failure of all models to their inability to capture shifts in the specific nature of nutrient limitation. Our results point to more complex linkages between multinutrient limitation and cellular resource allocation than currently parameterized in models. These results suggest a greater importance of understanding the interaction between the type of nutrient limitation and plankton diversity for predicting the global variation in surface C:N:P.

Stable isotope patterns of mesopelagic communities over two shallow seamounts of the south-western Indian Ocean

The stable carbon (δ13C) and nitrogen (δ15N) isotope values of soft tissues of micronekton (crustaceans, squid, mesopelagic fish) and zooplankton were measured from organisms collected on the RV Antea at two seamounts located in the south-western Indian Ocean: La Pérouse (summit depth ~60 m) and “MAD-Ridge” (thus named in this study; summit depth ~240 m). Surface particulate organic matter (POM-Surf) showed higher δ13C at the more productive MAD-Ridge than at the oligotrophic La Pérouse seamount. Particulate organic matter and zooplankton were depleted in 15N at La Pérouse pinnacle compared with MAD-Ridge. Gelatinous organisms and crustaceans occupied the lowest and intermediate trophic levels (TL ~2 and 3 respectively) at both seamounts. Mesopelagic fish and smaller-sized squid sampled at both seamounts occupied TL ~3 to 4, whereas the large nektonic squid, Ommastrephes bartramii, collected at MAD-Ridge only, exhibited a TL of ~5. The δ15N values of common open-water mesopelagic taxa were strongly influenced by specimen size and feeding habits at both seamounts, with an increase in δ15N values with increasing size. Carnivorous fish species sampled exclusively over the seamounts’ flanks and summits exhibited TL values of ~4, irrespective of their wide size ranges. The work could not demonstrate any differences in δ13C values of mesopelagic fish between the seamounts and the surrounding oceanic areas. The study segregated clusters of mesopelagic organisms according to their δ13C and δ15N values, with variations in stable isotope values reflecting a complex range of processes possibly linked to productivity as well as biological and ecological traits of the species (size and feeding mode).

Stable Carbon Isotope Signature of Particulate Organic Matter in the Southwestern Sumatran Waters of the Eastern Indian Ocean

The Southwestern Sumatran Waters of the Eastern Indian Ocean are known to be affected by the South Java Current and the South Equatorial Counter Current. Many studies have been carried out in relation to upwelling and the Indonesian Through Flow. However, there has been no systematic study into the properties of the particulate organic matter in the Southwestern Sumatran Waters. Therefore, the organic matter in these waters in terms of its origin is unknown. As part of the Widya Nusantara Expedition 2015 research cruise, this study aimed to examine the stable isotope ?13C signature of particulate organic matter (POM), especially with regards to the origins of the organic matter. The stable isotope ?13C is complemented by other variables such as chlorophyll-a, particulate organic carbon (POC), and nutrients (phosphate, silicate, ammonium and nitrate). The POC tends to be depth-dependent. The values of ?13C are ?23.56, ?24.30 and ?24.06‰ for 5, 100 and 300 m depths, respectively. We found that POM tended to be isotopically lighter with increasing POC and chl-a, especially in the surface water, potentially due to the preferential lighter carbon isotope for metabolism by the primary producer. The origin of POM in the Southwestern Sumatran waters is marine end-member in the surface (up to 100 m depth) and mixed compositions at the surface of twilight zone (100–300 m depth). The next layer, i.e. twilight zone (more than 300 m depth), is terrigenous end-member. The surface POM of SSW, as shown in 5 m depth, is not freshly produced and tends to be either autochthonous or allochthonous.

The unique ecological role of pyrosomes in the Eastern Tropical Pacific

AbstractPyrosomes are an important but often overlooked component of marine zooplankton communities, with limited existing information regarding their ecological and trophic roles in pelagic ecosystems. We present the first estimates of grazing and trophic interactions of the large tropical pyrosome, Pyrostremma spinosum, in the Eastern Tropical Pacific. While patchy in distribution, Pyrostremma spinosum's grazing impact was substantial, up to 17.5% of chlorophyll a standing stock d−1 in certain areas. In contrast, these organisms cleared a very small percentage of the abundant picoplankton Synechococcus spp. compared to the bulk zooplankton community. Stable isotopes (13C and 15N) indicated that particulate organic matter (POM) from the surface mixed layer (0–20 m) constitutes the isotopic food‐web baseline for most of the zooplankton community, and zooplankton trophic interactions were size structured in some areas. Pyrosomes, doliolids, and appendicularians, along with the smallest size class of net‐collected zooplankton, had isotopic values closest to pure herbivory, while intermediate size classes, copepods, and salps showed substantial omnivory/carnivory. Euphausiids, chaetognaths, and > 2 mm zooplankton were the main carnivorous zooplankton in the plankton food web. Stable isotopes indicated that Pyrostremma spinosum is trophically distinct from the rest of the zooplankton community, grazing just below the mixed layer (20–40 m), as opposed to feeding on surface POM. Pyrosomes represent an additional, distinct pathway for material transfer up the plankton food web, by directly consuming POM sources not substantially grazed upon by the rest of the mesozooplankton community.

Origin and composition of particulate organic matter in a macrotidal turbid estuary: The Gironde Estuary, France

At the interface between continent and ocean, estuaries receive particles, and especially particulate organic matter (POM) originating from these two reservoirs, but also produce POM, through autochthonous primary production. The origin and composition of surface POM in the Gironde Estuary (SW France) and the environmental forcing of its variability was investigated using the data set produced by the French Coastal Monitoring Network SOMLIT (Service d'Observation en Milieu LITtoral; monthly like sampling during years 2007–2009). This estuary is considered as a model of macrotidal turbid estuaries. Using elemental and isotopic composition of the POM, we estimated that, at the inner estuary space scale and inter-annual time scale, surface particulate organic carbon (POC) was composed of terrestrial POM originated from the turbidity maximum (96.4%; refractory POC) and flood events (1.6%; labile and refractory POC), and of riverine (0.1%), estuarine (0.8%) and marine (1.1%) phytoplankton, i.e. that POC was 98% and 2% of terrestrial and phytoplankton origin, respectively. However, there was a clear spatial gradient: the phytoplankton contribution increases from ca. 1% in the upper and middle estuary to 8.5% in the lower estuary, where light condition is more favourable to plankton growth. The low contribution of phytoplankton to the POC is a characteristic of the Gironde estuary and contrast with other large temperate estuaries. Statistical analysis indicates that salinity, river flow and SPM concentration, and thus associated hydro-dynamic and sedimentary processes, were the only environmental forcings to the composition of surface POC in this system, at intra- and inter-annual time scale. In contrast, temperature and nutrient concentrations, and thus associated processes, do not force this composition of POC.By combining POC fluxes entering the inner estuary (literature data), POC loss as dissolved organic carbon and CO2 and as sediment trapping within the inner estuary (literature data), and our estimate of the composition of POC flux at the mouth of the estuary (96% and 4% of terrestrial and phytoplankton origin), a first-order net export of POC originating from the Gironde to the continental shelf was estimated: it amounts 48,150tCyr−1, and is composed of 46,200tCyr−1 of terrestrial material and of 1950tCyr−1 of estuarine phytoplankton. POC exported by the Gironde Estuary is thus poorly bioavailable for shelf pelagic and benthic food webs.

Data assimilation with a local Ensemble Kalman Filter applied to a three-dimensional biological model of the Middle Atlantic Bight

A multivariate sequential data assimilation approach, the Localized Ensemble Kalman Filter (LEnKF), was used to assimilate daily satellite observations of ocean chlorophyll into a three-dimensional physical–biological model of the Middle Atlantic Bight (MAB) for the year 2006. Covariance localization was applied to make the EnKF analysis more effective by removing spurious long-range correlations in the ensemble approximation of the model's covariance. The model is based on the Regional Ocean Modeling System (ROMS) and coupled to a biological nitrogen cycle model, which includes seven state variables: chlorophyll, phytoplankton, nitrate, ammonium, small and large detrital nitrogen, and zooplankton. An ensemble of 20 model simulations, generated by perturbing the biological parameters according to assumed probability distributions, was used. Model fields of chlorophyll, phytoplankton, nitrate and zooplankton were updated at all vertical layers during LEnKF analysis steps, based on their cross-correlations with surface chlorophyll (the observed variable). The performance of the LEnKF scheme, its influence on the model's predictive skill and on surface particulate organic matter concentrations and primary production are investigated. Estimates of surface chlorophyll and particulate organic carbon are improved in the data-assimilative simulation when compared to one without any assimilation, as is the model's predictive skill.

Chemical qualification of electrophoretically detectable peptides and sugar chains in oceanic surface particulate organic matter

Particulate organic matter (POM) is a mixture of living POM (organisms) and non-living POM (detritus). Since the majority of amino acids in organisms are comprised of proteins, and since the particulate combined amino acids (PCAAs) liberated by the acid hydrolysis of POM is the largest constituent of POM, PCAAs may be a mixture of proteins in organisms and their degradation products in detritus. However, the early stage of degradation and chemical alteration of proteins and the processes by which proteins in organisms are transferred to detrital PCAAs have not been well documented. Here we use gel chromatography (SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis) to chemically characterize the PCAAs pool and the following results were obtained. 1) The protein/peptide-specific dye (Coomassie brilliant blue; CBB) stainable materials (CSM) and the sugar chain-specific periodic acid Schiff (PAS) stainable materials (PSM) were simultaneously detected on POM electrophoretograms from the Antarctic to the Tropical Zone. 2) CSM and PSM showed electrophoretograms very similar to each other, in that they exhibited a smeared-staining pattern with a broad molecular weight range on the SDS-PAGE gel. Nevertheless, they did not covalently bind each other, and they were roughly separated using the solubility of trichloroacetic acid (TCA) solution. 3) Results obtained from the combination of enzymatic and chemical deglycosylation experiments, solubility in TCA solution, and SDS-PAGE revealed that CSM might be a conglomeration of proteins/peptides of various organisms in POM, while PSM might be comprised of degradation products of glycoconjugates. Carbohydrate-rich remnants with small-sized peptide chains derived from O-linked glycoproteins and/or proteoglycans were considered to be the most likely chemical form of PSM. The possible roles of such sugar chains in marine environments are discussed.

Characteristics of suspended particulate organic matter in the southwestern Atlantic: Influence of temperature, nutrient and phytoplankton features on the stable isotope signature

Surface particulate organic matter (POM) along a transect from Subantarctic coastal waters on the Argentine shelf to the Bellingshausen Sea was characterized by its organic carbon (POC) and nitrogen (PON) content and δ 13C and δ 15N signatures in relation to sea surface water temperature (SST), nutrients and plankton. The correlation of δ 13C with SST was highly significant for the entire transect but less obvious within Subantarctic shelf ecosystems. Stable isotopes of POM varied from δ 13C ~ − 12‰ and δ 15N ~ 8‰ in Subantarctic shallow waters to δ 13C ~ − 32‰ and δ 15N ~ − 2‰ in the sector including the oceanic Subantarctic waters and the Antarctic region. In Argentine shelf waters δ 13C was > − 24‰ (on average − 20.9‰) and more variable than in oceanic Subantarctic and Antarctic waters (average of − 27.6‰). High isotopic variability of POM in northern Argentine shelf waters is probably due to a pronounced nutrient gradient. There, a sharp δ 13C decrease of ca. 12‰ was associated to an increase of the silicate to nitrate (Si:N) ratio to values > 0.25, and an increase of siliceous phytoplankton. Further south, Si:N ratios > 1 did not significantly affect δ 13C, and the influence of the sea surface temperature (SST) was more evident. δ 15N in POM of Argentine shelf waters averaged 6.3 ± 2.4‰, and the lowest δ 15N values (− 1.7‰) occurred in the northern Drake Passage, where they build, together with δ 13C around − 27‰, a clearly distinct pattern in the western South Atlantic. For the whole transect, SST alone accounted for 74% of the δ 13C variability. A multiple regression including SST, ammonium and POC explained 83% of δ 13C variance. The fit improvement by ammonium involved the nutrient-poor, regenerative system in the northernmost shallow sector and the Subantarctic shelf. δ 15N showed a strong inverse relationship with the fraction of unutilized nitrate, probably due to isotopic enrichment in the nitrate pool by phytoplankton uptake.

Dynamics and elemental stoichiometry of carbon, nitrogen, and phosphorus in particulate and dissolved organic pools during a phytoplankton bloom induced by in situ iron enrichment in the western subarctic Pacific (SEEDS-II)

The dynamics of organic carbon (C), nitrogen (N), and phosphorus (P) were examined during an in situ mesoscale iron-enrichment experiment in the western North Pacific in the summer of 2004. We separately determined the production of particulate organic matter (POM) and dissolved organic matter (DOM) and their subsequent removal during the bloom decline. As the iron-induced phytoplankton bloom progressed (days 0–14), POM increased in the surface mixed layer, while DOM did not increase significantly. The molar ratios for C:N, C:P, and N:P of the newly produced POM were estimated to be 4.9, 190, and 37 in the surface mixed layer, whereas the dissolved inorganic nitrogen to soluble reactive phosphorus drawdown ratio was 17. Preferential remineralization of P over C and N from the POM was postulated during the developing phytoplankton bloom. During the bloom decline (days 16–25), surface POM decreased with a similar C:N of 5.2. The N:P ratio of surface DOM increased during the bloom decline. Below the surface mixed layer, DOC and DON increased moderately after the peak of the bloom. The time-series variation of DOC and DON was not identical. The C, N, and P dynamics through the accumulation and removal of POM and DOM were complex. Grazing by mesozooplankton during the experiment may have played a significant role in the uncoupling of the dynamics of C, N, and P.

Comparison of C and N stable isotope ratios between surface particulate organic matter and microphytoplankton in the Gulf of Lions (NW Mediterranean)

Carbon and nitrogen stable isotope ratios of particulate organic matter (POM) in surface water and 63–200 μm-sized microphytoplankton collected at the fluorescence maximum were studied in four sites in the Gulf of Lions (NW Mediterranean), a marine area influenced by the Rhone River inputs, in May and November 2004. Some environmental (temperature, salinity) and biological (POM, Chlorophyll a and phaeopigments contents, phytoplankton biomass and composition) parameters were also analysed. Significantly different C and N isotopic signatures between surface water POM and microphytoplankton were recorded in all sites and seasons. Surface water POM presented systematically lower δ 13C (∼4.2‰) and higher δ 15N (∼2.8‰) values than those of microphytoplankton, due to a higher content of continental and detrital material. Seasonal variations were observed for all environmental and biological parameters, except salinity. Water temperature was lower in May than in November, the fluorescence maximum was located deeper and the Chlorophyll a content and the phytoplankton biomass were higher, along with low PON/Chl a ratio, corresponding to spring bloom conditions. At all sites and seasons, diatoms dominated the phytoplankton community in abundance, whereas dinoflagellate importance increased in autumn particularly in coastal sites. C and N isotopic signatures of phytoplankton did not vary with season. However, the δ 15N of surface water POM was significantly higher in November than in May in all sites likely in relation to an increase in 15N/ 14N ratio of the Rhone River POM which influenced surface water in the Gulf of Lions. As it is important to determine true baseline values of primary producers for analysing marine food webs, this study demonstrated that C and N isotopic values of surface water POM cannot be used as phytoplankton proxy in coastal areas submitted to high river inputs.

On the treatment of particulate organic matter sinking in large-scale models of marine biogeochemical cycles

Abstract. Various functions have been suggested and applied to represent the sedimentation and remineralisation of particulate organic matter (POM) in numerical ocean models. Here we investigate some representations commonly used in large-scale biogeochemical models: a constant sinking speed, a sinking speed increasing with depth, a spectrum of particles with different size and different size-dependent sinking velocities, and a model that assumes a power law particle size distribution everywhere in the water column. The analysis is carried out for an idealised one-dimensional water column, under stationary boundary conditions for surface POM. It focuses on the intrinsic assumptions of the respective sedimentation function and their effect on POM mass, mass flux, and remineralisation profiles. A constant and uniform sinking speed does not appear appropriate for simulations exceeding a few decades, as the sedimentation profile is not consistent with observed profiles. A spectrum of size classes, together with size-dependent sinking and constant remineralisation, causes the sinking speed of total POM to increase with depth. This increase is not strictly linear with depth. Its particular form will further depend on the size distribution of the POM ensemble at the surface. Assuming a power law particle size spectrum at the surface, this model results in unimodal size distributions in the ocean interior. For the size-dependent sinking model, we present an analytic integral over depth and size that can explain regional variations of remineralisation length scales in response to regional patterns in trophodynamic state.

D/H ratios of fatty acids from marine particulate organic matter in the California Borderland Basins

We report the molecular and hydrogen–isotopic compositions of fatty acids extracted from suspended particulate organic matter (POM) and surface sediments at three stations off the southern California coast: Santa Barbara Basin, Santa Monica Basin, and the Gulf of Santa Catalina. Values of δD for individual fatty acids ranged from −237‰ to −73‰ in POM and from −216‰ to −124‰ in sediments. For most fatty acids, there are no significant differences in δD between sampling locations, with depth at each location, or between POM and sediments. Two fatty acids of likely bacterial origin ( i-15:0, 15:0) are strongly D enriched in all samples, while a third ( cyc-17:0) is not. The origins of that enrichment are uncertain, and could reflect either an anomalous D/H fractionation in certain marine bacteria, or a significant terrestrial source for those fatty acids, or both. In surface POM and sediments, even carbon numbered fatty acids become slightly D enriched as chain length increases. This isotopic ordering is similar to that observed in living organisms, and is presumably biosynthetic in origin. In contrast, all POM samples from below the mixed layer show a consistent pattern of D depletion with increasing chain length. The order of D enrichment in these fatty acids is well correlated with their solubility, and may be caused by fractionations accompanying dissolution or degradation by microbes.

Chemical forms and dynamics of amino acid-containing particulate organic matter in Pacific surface waters

Particulate combined amino acids (PCAA) are the most abundant identified constituents of particulate organic matter (POM) in Pacific Ocean surface waters, but their chemical forms are unclear. In the present study, chemical characterization of amino acid-containing materials in surface POM from subarctic to subtropical waters along 165 °E in the Pacific was carried out by one- and two-dimensional gel electrophoresis. At least four chemical forms of amino acid-containing POM were distinguished: proteins, acidic materials containing peptides, protein/peptide-specific dye-stainable low-molecular-mass materials (stainable materials) and non-stainable materials, all of which were considered to be major components of detrital POM. Seventeen distinct protein containing components were distinguished in samples across the transect. A majority of stainable materials was estimated to comprise 6–8 amino acid residues, while less than six amino acid residues made up the non-stainable materials. Among the four chemical forms, acidic materials and non-stainable materials were major components, accounting for 31–42% and 49–63% of PCAA, respectively, along the transect. Proteins were common, but they were quantitatively less than 2% of PCAA. Stainable materials were regionally variable and more abundant in subarctic waters than in subtropical waters. The mechanistic processes by which such amino acid-containing POM occurs as detrital POM are discussed.

Variability of unusual distributions of alkenones in the surface waters of the Nordic seas

Samples of filtered particulate organic matter (POM) were obtained during the summers of 1999 and 2000 from the surface waters of the Nordic seas to monitor the spatial distribution of long‐chain alkenones. The aim of the study was to appraise existing alkenone‐based climatic proxies in northern high latitudes. Unusually high percentages of the tetraunsaturated alkenone were measured in the polar waters of the East Greenland Current, with C37:4 of up to 77% in 80% of sea‐ice cover. Values of percent C37:4 across the Nordic seas showed a strong association with water mass type. Analysis of coccoliths in filters indicated that calcified Emiliania huxleyi could not be discounted as the biological precursor of alkenones in all the water masses. A combined data set of 69 samples of POM revealed a stronger correlation of percent C37:4 to sea surface salinity (SSS; R2 = 0.72) than to sea surface temperature (SST; R2 = 0.50). Values of percent C37:4 in sea surface POM were much higher than those in surficial sediments of the northern North Atlantic. To explain the discrepancy in sedimentary and surface water column percent C37:4, we propose that the alkenone contents in surface sediments underlying arctic and polar waters are a combination of autochthonous and allochthonous inputs of alkenones. Our results show that percent C37:4 can be used to reconstruct the relative extension of arctic/polar water masses in the North Atlantic. However, the results prevent confirmation of percent C37:4 as a paleo‐SSS proxy in the Nordic seas, given its multivariate nature in our data set and the decoupling between its range of values in surface waters and sediments.

Radiocarbon evidence for annual growth rings in the deep-sea octocoral Primnoa resedaeformis

The deep-sea gorgonian octocoral Primnoa resedaeformis is distributed throughout the Atlantic and Pacific Oceans at depths of 65-3200 m. It has a two-part skeleton of calcite and gorgonin. Towards the inside of the axial skeleton gorgonin and calcite are deposited in concentric growth rings, similar to tree rings. Colonies were collected from the Northeast Channel (northwest Atlantic Ocean, southwest of Nova Scotia, Canada) from depths of 250-475 m. Radiocarbon was measured in individual rings isolated from sections of each colony, after dissolution of calcite. Each {Delta}{sup 14}C measurement was paired with a ring age determined by three amateur ring counters. The precision of ring counts averaged better than {+-} 2 years. Accurate reconstruction of 20th century bomb-radiocarbon shows that (1) the growth rings are formed annually, (2) the gorgonin is derived from surface particulate organic matter (POM) and (3) useful environmental data are recorded in the organic endoskeletons of deep-sea octocorals. These results support the use of Primnoa resedaeformis as a long-term, high resolution monitor of surface ocean conditions, particularly in temperate and boreal environments where proxy data are lacking.

Potential climate signals from the deep-sea gorgonian coral Primnoa resedaeformis

The deep-sea gorgonian coral Primnoa resedaeformis has an arborescent skeleton composed of both calcite and a horn-like structural protein called gorgonin. We have investigated potential climate records in corals from Alaska, the eastern seaboard of Canada and the United States, and a Southern Ocean (Pacific sector) seamount. Temperatures at these sites range from 4 to ∼10 °C. δ18O values of the calcite show strong evidence for isotopic disequilibrium. Extraction of δ18O paleotemperatures is therefore not straightforward. Sr/Ca data, analyzed by Secondary Ion Mass Spectrometry (SIMS), suggest that temperature might be a control on calcite Sr/Ca in Primnoa resedaeformis, but that growth-related kinetic effects could also be important. Based on previous 14C, δ13C and δ15N measurements, it has been suggested that particulate organic matter (POM) from the surface is an important carbon source to the polyps and the gorgonin fraction of the Primnoa skeleton. δ15N and δ13C of polyps and gorgonin show similar regional differences to δ15N and δ13C of surface POM. Polyps and contemporaneous gorgonin correlate strongly for both δ13C and δ15N. The influence of nutrient isotopic composition and climate and productivity variations on the isotopic composition of surface POM may therefore be recorded in gorgonin layers. These corals have very long lifespans (several centuries). The potential exists, therefore, to obtain extended records of surface productivity, deep ocean temperature and chemistry of value to climatologists and fisheries managers.

Primary productivity and nutrient utilization ratios in the Pacific sector of the Southern Ocean based on seasonal changes in seawater chemistry

In the austral winter (September–October) of 1994, a hydrographic cruise in the Pacific sector of the Southern Ocean (NBP94-5) was completed, complementing two austral summer cruises (February–March) in 1992 (WOCE S4-P) and 1994 (NBP94-2) in the same area. During all three cruises, the partial pressure of carbon dioxide and concentration of total carbon dioxide dissolved in seawater were determined throughout the water column, accompanied by oxygen and nutrient measurements. Seasonal changes in CO 2 and nutrients observed in the mixed layer above the remnant winter water were used to estimate utilization ratios, primary productivity, and new production. The mean rate of primary production over 120 days ranged from 6 to 24 mmol C m -2d -1, consistent with the notion of the Southern Ocean as a low productivity area. Primary production was highest in the northern limb of the Ross Sea Gyre, where the wintertime vertical stability of the upper water column was lower. The circulation patterns and nutrient distributions in the region studied appear to influence the primary production rates observed. The ratio of biogenic silica to carbon was found to be 0.66±0.02. The observed N/P utilization ratio of 13.0±1.2 and C/P utilization ratio of 91.4±7.9 are both significantly lower than the traditional Redfield ratios of 16 and 106, respectively. The former is, however, consistent with the ΔN/ΔP regeneration ratio of 14.0±0.3 discerned for deep waters south of the Polar Front. Hence, the classical C/P and N/P Redfield ratios do not appear to hold in Antarctic waters. On the other hand, the C/N utilization ratio of 6.9±0.6 does agree with the Redfield ratio of 6.6 (106/16). This C/N ratio also agrees with the ratio obtained for surface particulate organic matter (POM) taken during the WOCE S4-P cruise along 67°S. Accordingly, the biological cycles of carbon and nitrogen in the Southern Ocean appear to be “Redfieldian”.