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  • Nature Research  (50)
  • American Geophysical Union
  • American Institute of Physics (AIP)
  • American Meteorological Society
  • 2020-2024  (72)
  • 1960-1964
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  • 2020  (72)
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  • 1
    Publication Date: 2023-03-08
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125(5), (2020): e2019JC016007, doi:10.1029/2019JC016007.
    Description: Benthic inputs of nutrients help support primary production in the Chukchi Sea and produce nutrient‐rich water masses that ventilate the halocline of the western Arctic Ocean. However, the complex biological and redox cycling of nutrients and trace metals make it difficult to directly monitor their benthic fluxes. In this study, we use radium‐228, which is a soluble radionuclide produced in sediments, and a numerical model of an inert, generic sediment‐derived tracer to study variability in sediment inputs to the Chukchi Sea. The 228Ra observations and modeling results are in general agreement and provide evidence of strong benthic inputs to the southern Chukchi Sea during the winter, while the northern shelf receives higher concentrations of sediment‐sourced materials in the spring and summer due to continued sediment‐water exchange as the water mass traverses the shelf. The highest tracer concentrations are observed near the shelfbreak and southeast of Hanna Shoal, a region known for high biological productivity and enhanced benthic biomass.
    Description: This study presents data from multiple Arctic expeditions over the past two decades, and we are indebted to the captains, crews, and scientific parties that made this data collection possible. This work was funded by NSF awards OCE‐1458305 to M. Charette, OCE‐1458424 to W. Moore, OCE‐1434085 to D. Kadko, PLR‐1504333 to R. Pickart, and OPP‐1822334 to M. Spall. Funding was also provided by National Oceanic and Atmospheric Administration Grant NA14‐OAR4320158 to R. Pickart. L. Kipp was supported by an Ocean Frontier Institute Postdoctoral Fellowship. Radium data used in this manuscript are available in Table S1.
    Description: 2020-10-27
    Keywords: Chukchi Sea ; Benthic flux ; Radium‐228 ; GEOTRACES
    Repository Name: Woods Hole Open Access Server
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  • 2
    Publication Date: 2023-02-08
    Description: Diverse microbial ecosystems underpin life in the sea. Among these microbes are many unicellular eukaryotes that span the diversity of the eukaryotic tree of life. However, genetic tractability has been limited to a few species, which do not represent eukaryotic diversity or environmentally relevant taxa. Here, we report on the development of genetic tools in a range of protists primarily from marine environments. We present evidence for foreign DNA delivery and expression in 13 species never before transformed and for advancement of tools for eight other species, as well as potential reasons for why transformation of yet another 17 species tested was not achieved. Our resource in genetic manipulation will provide insights into the ancestral eukaryotic lifeforms, general eukaryote cell biology, protein diversification and the evolution of cellular pathways.
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  • 3
    Publication Date: 2023-02-08
    Description: Atlantic cod (Gadus morhua) is one of the most important fish species in northern Europe for several reasons including its predator status in marine ecosystems, its historical role in fisheries, its potential in aquaculture and its strong public profile. However, due to over-exploitation in the North Atlantic and changes in the ecosystem, many cod populations have been reduced in size and genetic diversity. Cod populations in the Baltic Proper, Kattegat and North Sea have been analyzed using a species specific single nucleotide polymorphism (SNP) array. Using a subset of 8,706 SNPs, moderate genetic differences were found between subdivisions in three traditionally delineated cod management stocks: Kattegat, western and eastern Baltic. However, an FST measure of population differentiation based on allele frequencies from 588 outlier loci for 2 population groups, one including 5 western and the other 4 eastern Baltic populations, indicated high genetic differentiation. In this paper, differentiation has been demonstrated not only between, but also within western and eastern Baltic cod stocks for the first time, with salinity appearing to be the most important environmental factor influencing the maintenance of cod population divergence between the western and eastern Baltic Sea.
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  • 4
    Publication Date: 2023-02-08
    Description: The Sea of Galilee in northeast Israel is a freshwater lake filling a morphological depression along the Dead Sea Fault. It is located in a tectonically complex area, where a N-S main fault system intersects secondary fault patterns non-univocally interpreted by previous reconstructions. A set of multiscale geophysical, geochemical and seismological data, reprocessed or newly collected, was analysed to unravel the interplay between shallow tectonic deformations and geodynamic processes. The result is a neotectonic map highlighting major seismogenic faults in a key region at the boundary between the Africa/Sinai and Arabian plates. Most active seismogenic displacement occurs along NNW-SSE oriented transtensional faults. This results in a left-lateral bifurcation of the Dead Sea Fault forming a rhomb-shaped depression we named the Capharnaum Trough, located off-track relative to the alleged principal deformation zone. Low-magnitude (ML = 3–4) epicentres accurately located during a recent seismic sequence are aligned along this feature, whose activity, depth and regional importance is supported by geophysical and geochemical evidence. This case study, involving a multiscale/multidisciplinary approach, may serve as a reference for similar geodynamic settings in the world, where unravelling geometric and kinematic complexities is challenging but fundamental for reliable earthquake hazard assessments.
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  • 5
    Publication Date: 2023-02-08
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  • 6
    Publication Date: 2023-02-08
    Description: Bathymetry (seafloor depth), is a critical parameter providing the geospatial context for a multitude of marine scientific studies. Since 1997, the International Bathymetric Chart of the Arctic Ocean (IBCAO) has been the authoritative source of bathymetry for the Arctic Ocean. IBCAO has merged its efforts with the Nippon Foundation-GEBCO-Seabed 2030 Project, with the goal of mapping all of the oceans by 2030. Here we present the latest version (IBCAO Ver. 4.0), with more than twice the resolution (200 × 200 m versus 500 × 500 m) and with individual depth soundings constraining three times more area of the Arctic Ocean (∼19.8% versus 6.7%), than the previous IBCAO Ver. 3.0 released in 2012. Modern multibeam bathymetry comprises ∼14.3% in Ver. 4.0 compared to ∼5.4% in Ver. 3.0. Thus, the new IBCAO Ver. 4.0 has substantially more seafloor morphological information that offers new insights into a range of submarine features and processes; for example, the improved portrayal of Greenland fjords better serves predictive modelling of the fate of the Greenland Ice Sheet.
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  • 7
    Publication Date: 2023-02-08
    Description: Climate change has led to a ~ 40% reduction in summer Arctic sea-ice cover extent since the 1970s. Resultant increases in light availability may enhance phytoplankton production. Direct evidence for factors currently constraining summertime phytoplankton growth in the Arctic region is however lacking. GEOTRACES cruise GN05 conducted a Fram Strait transect from Svalbard to the NE Greenland Shelf in summer 2016, sampling for bioessential trace metals (Fe, Co, Zn, Mn) and macronutrients (N, Si, P) at ~ 79°N. Five bioassay experiments were conducted to establish phytoplankton responses to additions of Fe, N, Fe + N and volcanic dust. Ambient nutrient concentrations suggested N and Fe were deficient in surface seawater relative to typical phytoplankton requirements. A west-to-east trend in the relative deficiency of N and Fe was apparent, with N becoming more deficient towards Greenland and Fe more deficient towards Svalbard. This aligned with phytoplankton responses in bioassay experiments, which showed greatest chlorophyll-a increases in + N treatment near Greenland and + N + Fe near Svalbard. Collectively these results suggest primary N limitation of phytoplankton growth throughout the study region, with conditions potentially approaching secondary Fe limitation in the eastern Fram Strait. We suggest that the supply of Atlantic-derived N and Arctic-derived Fe exerts a strong control on summertime nutrient stoichiometry and resultant limitation patterns across the Fram Strait region.
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  • 8
    Publication Date: 2023-02-08
    Description: More than half of Earth’s freshwater resources are held by the Antarctic Ice Sheet, which thus represents by far the largest potential source for global sea-level rise under future warming conditions1. Its long-term stability determines the fate of our coastal cities and cultural heritage. Feedbacks between ice, atmosphere, ocean, and the solid Earth give rise to potential nonlinearities in its response to temperature changes. So far, we are lacking a comprehensive stability analysis of the Antarctic Ice Sheet for different amounts of global warming. Here we show that the Antarctic Ice Sheet exhibits a multitude of temperature thresholds beyond which ice loss is irreversible. Consistent with palaeodata2 we find, using the Parallel Ice Sheet Model3,4,5, that at global warming levels around 2 degrees Celsius above pre-industrial levels, West Antarctica is committed to long-term partial collapse owing to the marine ice-sheet instability. Between 6 and 9 degrees of warming above pre-industrial levels, the loss of more than 70 per cent of the present-day ice volume is triggered, mainly caused by the surface elevation feedback. At more than 10 degrees of warming above pre-industrial levels, Antarctica is committed to become virtually ice-free. The ice sheet’s temperature sensitivity is 1.3 metres of sea-level equivalent per degree of warming up to 2 degrees above pre-industrial levels, almost doubling to 2.4 metres per degree of warming between 2 and 6 degrees and increasing to about 10 metres per degree of warming between 6 and 9 degrees. Each of these thresholds gives rise to hysteresis behaviour: that is, the currently observed ice-sheet configuration is not regained even if temperatures are reversed to present-day levels. In particular, the West Antarctic Ice Sheet does not regrow to its modern extent until temperatures are at least one degree Celsius lower than pre-industrial levels. Our results show that if the Paris Agreement is not met, Antarctica’s long-term sea-level contribution will dramatically increase and exceed that of all other sources.
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  • 9
    Publication Date: 2023-02-08
    Description: Past changes in ocean 14C disequilibria have been suggested to reflect the Southern Ocean control on global exogenic carbon cycling. Yet, the volumetric extent of the glacial carbon pool and the deglacial mechanisms contributing to release remineralized carbon, particularly from regions with enhanced mixing today, remain insufficiently constrained. Here, we reconstruct the deglacial ventilation history of the South Indian upwelling hotspot near Kerguelen Island, using high-resolution 14C-dating of smaller-than-conventional foraminiferal samples and multi-proxy deep-ocean oxygen estimates. We find marked regional differences in Southern Ocean overturning with distinct South Indian fingerprints on (early de-)glacial atmospheric CO2 change. The dissipation of this heterogeneity commenced 14.6 kyr ago, signaling the onset of modern-like, strong South Indian Ocean upwelling, likely promoted by rejuvenated Atlantic overturning. Our findings highlight the South Indian Ocean’s capacity to influence atmospheric CO2 levels and amplify the impacts of inter-hemispheric climate variability on global carbon cycling within centuries and millennia.
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  • 10
    Publication Date: 2023-02-08
    Description: Benthic fauna refers to all fauna that live in or on the seafloor, which researchers typically divide into size classes meiobenthos (32/64 µm–0.5/1 mm), macrobenthos (250 µm–1 cm), and megabenthos (〉1 cm). Benthic fauna play important roles in bioturbation activity, mineralization of organic matter, and in marine food webs. Evaluating their role in these ecosystem functions requires knowledge of their global distribution and biomass. We therefore established the BenBioDen database, the largest open-access database for marine benthic biomass and density data compiled so far. In total, it includes 11,792 georeferenced benthic biomass and 51,559 benthic density records from 384 and 600 studies, respectively. We selected all references following the procedure for systematic reviews and meta-analyses, and report biomass records as grams of wet mass, dry mass, or ash-free dry mass, or carbon per m2 and as abundance records as individuals per m2. This database provides a point of reference for future studies on the distribution and biomass of benthic fauna.
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