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Reconstructions of ocean primary productivity (PP) help to explain past and present biogeochemical cycles and climate changes in the oceans. We document PP variations over the last 50 kyr in a currently oligotrophic subtropical region, the Gulf of Cadiz. Data combine refined results from previous investigations on dinocyst assemblages, alkenones, and stable isotopes ( 18O, 13C) in planktonic (Globigerina bulloides) and endobenthic (Uvigerina mediterranea) foraminifera from cores MD04-2805 CQ and MD99-2339, with new isotopic measurements on epibenthic (Cibicides pachyderma–Cibicidoides wuellerstorfi) foraminifera and dinocyst-based estimates of PP using the new n = 1,968 modern database. We constrain PP variations and export production by integrating qualitative information from bio-indicators with dinocyst-based quantitative reconstructions such as PP and seasonal sea-surface temperature and information about remineralization from the benthic  13C (difference between epi- and endo-benthic foraminiferal  13C signatures). This study also includes new information on alkenone-based SST and total organic carbon which provides insights into the relationship between past regional hydrological activity and PP regime change. We show that PP, carbon export, and remineralization were generally high in the NE subtropical Atlantic Ocean during the last glacial period and that the Last Glacial Maximum (LGM) had lower  13C than the Heinrich Stadials with sustained high PP, likely allowing enhanced carbon sequestration. We link these PP periods to the dynamics of upwelling, active almost year-round during stadials, but restricted to spring-summer during interstadials and LGM, like today. During interstadials, nutrient advection through freshwater inputs during autumn–winter needs also to be considered to fully understand PP regimes. info:eu-repo/semantics/publishedVersion

To identify the dietary composition and characteristics of both Adélie (Pygoscelis adeliae) and Emperor (Aptenodytes forsteri) penguins at four breeding sites, we performed stable carbon (δ13C) and nitrogen (δ15N) isotope analysis of down samples taken from penguin chicks. Adélie Penguin chicks at Cape Hallett mostly fed on Antarctic krill (Euphausia superba, 65.5 ± 3.5%), a reflection of the prevalence of that species near Cape Hallett, and no significant differences were noted between 2017 and 2018. However, Adélie Penguin chicks at Inexpressible Island, located near Terra Nova Bay, fed on both Antarctic silverfish (Pleuragramma antarctica, 42.5%) and ice krill (Euphausia crystallorophias, 47%), reflecting the high biomass observed in Terra Nova Bay. Meanwhile, no significant difference was noted between the two breeding sites of the Emperor Penguin. Emperor Penguin chicks predominantly fed on Antarctic silverfish (74.5 ± 2.1%) at both breeding sites (Cape Washington and Coulman Island), suggesting that diet preference represents the main factor influencing Emperor Penguin foraging. In contrast, the diet of the Adélie Penguin reflects presumed regional differences in prey prevalence, as inferred from available survey data.

The concentration of n-alkanes (C17–C35) and sterols in marine particulate matter were investigated to trace the origin of organic carbon in Kongsfjorden in early spring (April). The spatial distributions of environmental factors (seawater temperature, salinity, density, turbidity, chlorophyll a (chl. a) and particulate organic carbon (POC) concentrations) and the cell density of phytoplankton differed between the inner and outer fjord regions. In addition, brassicasterol, diatom biomarker, showed a high concentration in the outer fjord and positive correlations with the chl. a and POC concentrations in the water column. In contrast, some sterols originating from terrestrial organic matter (OM), such as stigmasterol and campesterol, showed relatively higher concentrations in the inner fjord than in the outer fjord. Based on the distance-based redundancy analysis (db-RDA) result, the distributions of organic compounds are predominantly controlled by the water density and the POC and chl. a concentrations, and these distributions allowed us to divide the inner and outer fjord regions. However, the hierarchical clustering of principal components (HCPC) results obtained based on principal component analysis (PCA) using lipid biomarkers (C17–C35 alkanes and sterols) and environmental factors indicated that the clusters were distinguished by surface (0 m) and subsurface (>4 m) seawater samples rather than by any regional division. Notably, the concentration of relatively short-chain alkanes (average chain length (ACL): 24.6 ± 3.7) without a carbon preference for odd numbers (carbon preference index (CPI): 0.97 ± 0.11) in the sea surface layer was significantly higher than that of subsurface seawater (ACL: 31.1 ± 0.5 and CPI: 1.06 ± 0.03) in the early spring. This suggests the potential of these compounds as indicators for tidewater glacier-derived OM and freshwater input by snow melt into the fjord system. Hence, these results demonstrate that the distributions of lipid biomarkers in the water column possibly provide important information for a comprehensive understanding of the origin and transport of OM in an Arctic fjord.

Simple Summary Under limited resources, different species may coexist by segregating their food items and foraging time, but neighboring colonies within the same species may have highly overlapping foraging habits. Thus, it is hypothesized that intra-specific competition is more intense than the inter-specific competition. To test this hypothesis, we chose sympatrically breeding Chinstrap and Gentoo penguins at two neighboring colonies and tracked their foraging space and dive depths during chick-rearing. Here we report that there was a larger overlap in the foraging space between the two species than within each species, whereas there was lower inter-specific isotopic niche overlap than intra-specific isotopic niche overlap. Despite the low intra-specific spatial overlap, diets of conspecifics remained similar, resulting in the higher isotopic niche overlaps. Our results suggest that intra-specific competition is higher than inter-specific competition due to a lack of niche partitioning. Abstract Theory predicts that sympatric predators compete for food under conditions of limited resources. Competition would occur even within the same species, between neighboring populations, because of overlapping foraging habits. Thus, neighboring populations of the same species are hypothesized to face strong competition. To test the hypothesis that intra-specific competition is more intense than inter-specific competition owing to a lack of niche partitioning, we estimated the foraging area and diving depths of two colonial seabird species at two neighboring colonies. Using GPS and time-depth recorders, we tracked foraging space use of sympatric breeding Chinstrap and Gentoo penguins at Ardley Island (AI) and Narębski Point (NP) at King George Island, Antarctica. GPS tracks showed that there was a larger overlap in the foraging areas between the two species than within each species. In dive parameters, Gentoo penguins performed deeper and longer dives than Chinstrap penguins at the same colonies. At the colony level, Gentoo penguins from NP undertook deeper and longer dives than those at AI, whereas Chinstrap penguins did not show such intra-specific differences in dives. Stable isotope analysis of δ13C and δ15N isotopes in blood demonstrated both inter- and intra-specific differences. Both species of penguin at AI exhibited higher δ13C and δ15N values than those at NP, and in both locations, Gentoo penguins had higher δ13C and lower δ15N values than Chinstrap penguins. Isotopic niches showed that there were lower inter-specific overlaps than intra-specific overlaps. This suggests that, despite the low intra-specific spatial overlap, diets of conspecifics from different colonies remained more similar, resulting in the higher isotopic niche overlaps. Collectively, our results support the hypothesis that intra-specific competition is higher than inter-specific competition, leading to spatial segregation of the neighboring populations of the same species.

Analysis of the biochemical composition (carbohydrates, CHO, proteins, PRT, lipids, LIP) of particulate organic matter (POM, mainly phytoplankton) is used to assess trophic states, and the quantity of food material is generally assessed to determine bioavailability, however, bioavailability is reduced or changed by enzymatic hydrolysis. Here, we investigated the current trophic state and bioavailability of phytoplankton in the Chukchi Sea (including the Chukchi Borderland) during the summer of 2017. Based on a cluster analysis, our 12 stations were divided into three groups: the southern, middle, and northern parts of the Chukchi Sea. A principal component analysis (PCA) revealed that relatively nutrient-rich and high-temperature waters in the southern part of the Chukchi Sea enhanced the microphytoplankton biomass, while picophytoplankton were linked to a high contribution of meltwater derived from sea ice melting in the northern part of the sea. The total PRT accounted for 41.8% (&plusmn, 7.5%) of the POM in the southern part of the sea, and this contribution was higher than those in the middle (26.5 &plusmn, 7.5%) and northern (26.5 &plusmn, 10.6%) parts, whereas the CHO accounted for more than half of the total POM in the northern parts. As determined by enzymatic hydrolysis, LIP were more rapidly mineralized in the southern part of the Chukchi Sea, whereas CHO were largely used as source of energy for higher trophic levels in the northern part of the Chukchi Sea. Specifically, the bioavailable fraction of POM in the northern part of the Chukchi Sea was higher than it was in the other parts. The findings indicate that increasing meltwater and a low nutrient supply lead to smaller cell sizes of phytoplankton and their taxa (flagellate and green algae) with more CHO and a negative effect on the total concentration of POM. However, in terms of bioavailability (food utilization), which determines the rate at which digested food is used by consumers, potentially available food could have positive effects on ecosystem functioning.

We assessed the applicability of the nutrient diol index (NDI) as a proxy for sea surface nutrients by analyzing sediments from a box core (ES14-BC03) collected in the southwestern continental slope of the East Sea, or the Japan Sea (hereafter the East Sea). The estimated sedimentation rate based on the 210Pb chronology was 0.15 cm yr−1 over the last 240 yrs. The NDI-derived phosphate (0.69 μmol L−1) and nitrate (8.63 μmol L−1) concentrations for the core-top sediment were within the average phosphate (0.26 ± 0.08 μmol L−1) and nitrate (3.38 ± 2.32 μmol L−1) concentration ranges for the last ∼20 years, accounting for both estimation error and variation in observational data. The distributions of the NDI-diols varied slightly through time, grouping into two distinct clusters (Cluster 1 and Cluster 2) in both principle component analysis (PCA) and hierarchical clustering of principal components (HCPC). Cluster 2 represented a time period with higher relative abundances of the C28 and C30 1,14-diols, resulting in higher NDI-derived nutrient concentrations than those of other periods. Interestingly, during this period, the U 37 K ' -derived sea surface temperatures (SSTs) also decreased. These results indicate that higher surface nutrient conditions and colder SSTs occurred between 1884 CE and 1911 CE, which might be associated with stronger upwelling intensity at the study site. This study is the first application of the NDI to a down-core, demonstrating that the NDI can be a useful proxy that provides helpful information about past sea surface nutrient conditions.

Long chain alkyl diols (LCDs) have previously been used to develop several diol indices as a proxy for upwelling or stratification conditions and sea surface temperatures. However, there is still a lack of data on the distribution of LCDs in the Pacific Ocean, which calls into question to what extent these diol indices can serve as a proxy in the Pacific Ocean. Hence, we investigated the distribution of LCDs in suspended particulate matter (SPM) samples collected in July 2015 along a south-north transect ranging from the East Sea of Korea to the Bering Sea in the northwestern Pacific region. Our results showed that both saturated and unsaturated C28 and C30 1,14-diols were dominant in most SPM samples investigated. The principal component analysis (PCA) results of the SPM data revealed that the C28:1 and C30:1 1,14-diols were positively associated with nutrient concentrations. However, only the C28:1 1,14-diol in addition to the C28 1,14-diol was positively associated with nutrient concentrations in the global surface sediment data set previously published, while the C30:1 1,14-diol was related to sea surface temperature (SST). Based on these observations, we defined a new diol index, i.e., the nutrient diol index (NDI), which included the C28 1,14-diol as well as the C28:1 1,14-diol in the numerator and all the 1,13-, 1,14-, and 1,15-diols, excluding the C32 1,15-diol, in the denominator. The NDI was positively associated with the ocean atlas values of surface water phosphate and nitrate concentrations for the SPM and surface sediment data sets. Accordingly, the results of our study showed that the NDI has potential as a quantitative nutrient proxy for estimating sea surface phosphate (or nitrate) changes. Further studies should be undertaken in order to assess the applicability of the NDI as a paleo-nutrient proxy for confidently reconstructing surface water nutrient variations in the past, by analyzing more SPM, surface sediments, and sediment cores collected from various oceanic settings.

Drastic sea ice retreats in the Antarctic Peninsula, and the consequent environmental changes have brought about the consequences of biological adaptation and food competition. The isotopic niche is reflected by the ecological position and functional role of a species, which can be altered depending on these environmental changes. We assessed the isotopic niche and trophic positions (TP) of 3 seabirds on the Barton Peninsula, King George Island, Antarctica, to understand ecological interaction among the species. The average TP of Antarctic krill (Euphausia superba) (hereafter “krill”) (2.6 ± 0.1) was estimated by using the compiled published data of the compound-specific nitrogen isotope ratio of glutamic acid and phenylalanine in the Southern Ocean, and TP values of the seabirds based on that of krill to be reliable according to ecological knowledge. Our results on the overlap of the isotopic niches of seabirds suggests potential diet competition among the consumers, such as the brown skua (Stercorarius antarcticus) and south polar skua (Stercorarius maccormicki), whereas the distinct and broad isotopic niche width of kelp gulls (Larus dominicanus) suggesting that their adaptation through generalization was related to their extended habitat and various food sources. Our research indicates that isotopic niche of seabirds reflects their survival strategy for food competition. Consequently, these seabirds can be easily influenced by alternative food sources, including terrestrial and human-derived sources, by rapid environmental changes, indicating that they are valuable as key environmental species and require long-term monitoring in the Antarctic Peninsula.

We investigated the source, composition and reactivity of sedimentary organic carbon (OC) in a river-dominated continental marginal sea, the eastern Yellow Sea. A multi-proxy approach was applied to 9 riverbank sediments and 69 marine surface sediments, combining bulk and molecular organic parameters. The riverbank sediments (n=9) have on average low C/N ratio (4.8±0.5) and enriched δ13CTOC values (–21.5±0.6%) while the BIT index is on average 0.27. The sedimentary OC in the marine surface sediments appears to have a predominantly marine origin (on average C/N ratio=7.0±0.6 and δ13CTOC=–21.9±0.5%, n=69) with minor contribution of continental (i.e. soil- and lake/river-derived) OC (on average BIT index=0.00±0.01, n=69). However, the Δ14C values were depleted (on average –227±53%, n=8). Accordingly, our results highlight that fossil OC, potentially derived from erosion of sedimentary bedrocks in the catchment areas and/or human activities is being contributed to the sedimentary OC pool in the eastern Yellow Sea. More work is needed to better constrain the source, composition, and age of the organic material supplied to the eastern Yellow Sea, given the lack of biogeochemical data from the Korean rivers.

To investigate the effect of summer monsoon-derived inputs of particulate organic matter (POM) on patterns of stable isotopes in the food web in a reservoir, we traced dietary sources of carbon and nitrogen in pelagic zooplankton and herbivorous littoral zoobenthos following a monsoonal disturbance in Lake Paldang, a large regulated reservoir in Korea. Carbon and nitrogen stable isotopes were analyzed in POM, zooplankton, sedimentary organic matter, zoobenthos, and piscivorous fishes in pre- and post-summer monsoon periods. Sharp depletion of 13C and enrichment of 15N of POM along with elevated POC/Chl a ratios occurred following the summer monsoon period, reflecting the rapid reduction of phytoplankton biomass and a pulsed supply of terrestrial organic detritus. Herbivorous zooplankton δ13C values, which were initially similar to POM δ13C values in the pre-summer monsoon period, decreased to nearly that of terrestrial organic matter, providing isotopic evidence of allochthonous contribution to zooplankto...

Paleohydrological and paleoenvironmental changes were reconstructed using sedimentary records from the northern East China Sea, representing the past 15,000 years (from the last glacial period to the Holocene). The n -alkane distributions show many factors, from the changing origins (plant types) of organic matter input to marine sediments. Two climatic conditions were distinguished (warm/humid and cold/dry) by comparing the organic carbon isotope ratio (δ 13 C org ) with the reported planktonic foraminiferal oxygen isotope ratio (δ 18 O) of Globigerinoides ruber . A shift in the n -alkane-specific δ 13 C values reveals that the hydrological changes in the northern East China Sea were related to the carbon sources for aquatic macrophytes. The alkenone sea surface temperatures [SSTs (U K′ 37 )] record of the 07YSPC12 shows a range of 20.3 °C–26.5 °C (average 22.9 °C). Lower temperature SSTs were recorded during the Younger Dryas, with an average of 21.7 °C. The variation in the alkenone SSTs is interpreted to indicate the environmental conditions of the growth of alkenone synthesized organisms.

In this study, we aimed to reconstruct spring (April–June) sea ice changes in the western Arctic Ocean over recent centuries (ca. the last 250 years) by measuring biomarker distributions in a multicore (ARA01B-03MUC) retrieved from the Chukchi Shelf region and to evaluate outcomes against known or modelled estimates of sea ice conditions. Specifically, we analyzed for the Arctic sea ice proxy IP25 and assessed the suitability of a further highly branched isoprenoid (HBI) lipid (HBI III), epi-brassicasterol, and dinosterol as complementary biomarkers for use with the so-called phytoplankton marker-IP25 index (PIP25; PIIIIP25, PBIP25, and PDIP25, respectively). The presence of IP25 throughout core ARA01B-03MUC confirms the occurrence of seasonal sea ice at the study site over recent centuries. From a semi-quantitative perspective, all three PIP25 indices gave different trends, with some dependence on the balance factor c, a term used in the calculation of the PIP25 index. PIIIIP25-derived spring sea ice concentration (SpSIC) estimates using a c value of 0.63, determined previously from analysis of Barents Sea surface sediments, were likely most reliable, since SpSIC values were high throughout the record (SpSIC > 78%), consistent with the modern context for the Chukchi Sea and the mean SpSIC record of the 41 CMIP5 climate models over recent centuries. PBIP25-based SpSIC estimates were also high (SpSIC 108%−127%), albeit somewhat over-estimated, when using a c value of 0.023 obtained from a pan-Arctic distribution of surface sediments. In contrast, PDIP25 values using a pan-Arctic c value of 0.11, and PIP25 data based on the mean biomarker concentrations from ARA01B-03MUC, largely underestimated sea ice conditions (SpSIC as low as 13%), and exhibited poor agreement with instrumental records or model outputs. On the other hand, PBIP25 values using a c factor based on mean IP25 and epi-brassicasterol concentrations exhibited a decline towards the core top, which resembled recent decreasing changes in summer sea ice conditions for the Chukchi Sea; however, further work is needed to test the broader spatial generality of this observation.