The Amundsen Sea Polynya International Research Expedition (ASPIRE)

In search of an explanation for some of the greenest waters ever seen in coastal Antarctica and their possible link to some of the fastest melting glaciers and declining summer sea ice, the Amundsen Sea Polynya International Research Expedition (ASPIRE) challenged the capabilities of the US Antarctic Program and RVIB Nathaniel B. Palmer during Austral summer 2010–2011. We were well rewarded by both an extraordinary research platform and a truly remarkable oceanic setting. Here we provide further insights into the key questions that motivated our sampling approach during ASPIRE and present some preliminary findings, while highlighting the value of the Palmer for accomplishing complex, multifaceted oceanographic research in such a challenging environment

Repositioning of the global epicentre of non-optimal cholesterol

High blood cholesterol is typically considered a feature of wealthy western countries1,2. However, dietary and behavioural determinants of blood cholesterol are changing rapidly throughout the world3 and countries are using lipid-lowering medications at varying rates. These changes can have distinct effects on the levels of high-density lipoprotein (HDL) cholesterol and non-HDL cholesterol, which have different effects on human health4,5. However, the trends of HDL and non-HDL cholesterol levels over time have not been previously reported in a global analysis. Here we pooled 1,127 population-based studies that measured blood lipids in 102.6 million individuals aged 18 years and older to estimate trends from 1980 to 2018 in mean total, non-HDL and HDL cholesterol levels for 200 countries. Globally, there was little change in total or non-HDL cholesterol from 1980 to 2018. This was a net effect of increases in low- and middle-income countries, especially in east and southeast Asia, and decreases in high-income western countries, especially those in northwestern Europe, and in central and eastern Europe. As a result, countries with the highest level of non-HDL cholesterol�which is a marker of cardiovascular risk�changed from those in western Europe such as Belgium, Finland, Greenland, Iceland, Norway, Sweden, Switzerland and Malta in 1980 to those in Asia and the Pacific, such as Tokelau, Malaysia, The Philippines and Thailand. In 2017, high non-HDL cholesterol was responsible for an estimated 3.9 million (95 credible interval 3.7 million�4.2 million) worldwide deaths, half of which occurred in east, southeast and south Asia. The global repositioning of lipid-related risk, with non-optimal cholesterol shifting from a distinct feature of high-income countries in northwestern Europe, north America and Australasia to one that affects countries in east and southeast Asia and Oceania should motivate the use of population-based policies and personal interventions to improve nutrition and enhance access to treatment throughout the world. © 2020, The Author(s), under exclusive licence to Springer Nature Limited

Mapping phytoplankton iron utilization: Insights into Southern Ocean supply mechanisms

The emerging field of ocean iron biogeochemistry has prompted interest in the identification and quantification of Fe supply mechanisms. However, less attention has been given to estimating biological Fe utilization, and using the magnitude of Fe utilization to enhance our understanding of modes of supply. Here, we combine regionally validated data sets (1997-2007) on remotely sensed net primary production (NPP) with the iron:carbon (Fe:C) molar ratios for resident phytoplankton to produce Southern Ocean maps of Fe utilization. This approach exploits the resolution of remotely sensed data to investigate the spatial patterns, areal extent and interannual variability of Fe utilization, and relates it to published temporal and spatial trends for Fe supply mechanisms. We estimate that Southern Ocean Fe utilization averaged ∼3.3±0.3 × 108 μmol Fe a-1. This utilization varied little between years (7.8-9.6 μmol Fe m-2 a-1), was greatest for subpolar waters, particularly in the Atlantic (up to 53.0 μmol Fe m-2 a-1), and was lowest for the polar waters of the Indian sector. Application of maps corresponding to the location and areal extent of Fe supply regions (e.g., dust deposition) revealed that Fe utilization was highest in waters supplied by Patagonian dust, and to a lesser extent, where sediment resuspension (i.e. <500 m depth) probably supplies the majority of the Fe. The Atlantic sector has regions where multiple supply mechanisms are evident, resulting in perennially high productivity. This approach provides a better assessment of the relative importance, realm of influence, and areal extent of different Fe supply mechanisms to Southern Ocean waters

The organic complexation of iron in the Ross sea

The Ross Sea Polynya (RSP) has the highest primary production of Antarctic waters. Iron (Fe) is one of the most important growth limiting factors in the Southern Ocean. Dissolved iron (DFe)-binding organic ligands play an important ecological role because they increase the residence time of the scarce Fe. Therefore, we studied the DFe-binding organic ligands in the vicinity of the Ross Sea during a cruise between 20 December 2013 and 5 January 2014. The DFe-binding organic ligands were measured using Competing Ligand Exchange Cathodic Stripping Voltammetry (CLE-CSV) with TAC as competing ligand. The DFe-binding organic ligand concentrations always exceeded the DFe concentrations except in the bottom nepheloid layer of the RSP. No relationship was found between depth and DFe-binding organic ligand concentrations in the RSP indicating that these ligands are resistant to degradation and are probably exported by high salinity shelf water into the circumpolar current. DFe-binding organic ligand concentrations were highest in the RSP and the Antarctic Circumpolar Current (ACC) west of the Ross Sea, in association with seasonal phytoplankton blooms, although no correlation was found with parameters reflecting phytoplankton abundance or species. Phytoplankton sources and sinks of DFe-binding organic ligands are likely related to the seasonal progression of the bloom. In 39% of the samples, two DFe-binding organic ligand groups were distinguished based on the difference in binding strength. The distinction was especially clear in the RSP and in the ACC west of the RSP (54 and 77% of the samples, respectively) where blooms occurred and much less in the low biomass waters of the ACC east of the RSP and ice covered eastern part of the Ross Sea (15 and 10% of the samples, respectively). In these waters, other environmental factors, like sea ice melt, probably explain the absence of distinct relationships between primary production and ligand characteristics

Sources of iron in the Ross Sea Polynya in early summer

Dissolved Fe (DFe) was measured in the Ross Sea Polynya (RSP), Antarctica, during a GEOTRACES cruise between 20 December 2013 and 5 January 2014. DFe was measured over the full water column with special emphasis on samples near the seafloor. In the upper mixed layer, DFe was very low everywhere (< 0.10 nM). DFe increased with depth to values between 0.60 and 2.76 nM near the seafloor. The highest DFE concentrations were found at stations where a bottom nepheloid layer (BNL) was present (28 out of 32 stations). Deep DFe was lower (0.24–0.38 nM) at stations with no BNL. The main DFe supply to the upper mixed layer was vertical diffusive transport from the seafloor sediments, with a mean flux of 3.3 × 10- 8 mol DFe m- 2 day- 1. DFe fluxes showed large spatial variability of three orders of magnitude and were positively correlated to DFe concentrations near the sediment and vertical turbulent eddy diffusivity (Kz) and negatively correlated to water depth. The greatest fluxes were observed above the shallow banks such as Ross and Pennell Banks, and sediments with a BNL. We studied the horizontal diffusive transport from Franklin Island as an example of horizontal DFe transport from landmasses. No DFe transport was detected in the upper 100 m of the water column, probably due to uptake by phytoplankton. However, at 200 and 300 m depth, the DFe transport at distances between 50 and 100 km from Franklin Island was as large as the mean diffusive upward transport, indicating the potential importance of landmasses as a local source of DFe. Conversely, no horizontal transport of DFe from banks was detected. In addition, the Ross Ice Shelf (RIS) was a negligible source of DFe. Only the Ice Shelf Water (ISW), a water mass formed under the RIS, contained slightly elevated DFe (0.18–0.26 nM) compared to the surrounding waters. However, this elevated DFe did not reach into the RSP. Icebergs were not encountered and were not evaluated as a DFe source. Overall, we conclude that DFe from the seafloor and land mass sediments are the main DFe sources of DFe that support phytoplankton in the upper mixed layer of the Ross Sea Polynya in early summer

A Comparison of Global Estimates of Marine Primary Production From Ocean Color

The derivation of oceanic primary production using satellite measurements of ocean color (PP models) has great potential for biogeochemical studies. The Primary Production Algorithm Round Robin 3 (PPARR3) aims to compare existing PP models. It is a continuation of previous PPARR exercises, which compared in situ carbon14 uptake rates with an estimate of primary production using satellite-accessible data. PPARR2 found that modeled primary production would be within a factor of two of the in situ rates if systematic offsets were corrected. PPARR3 aims to provide a forum to compare model output, improve parameterization, and help identify the source of biases. This community project presently counts with over twenty modeling groups who estimate primary production for input fields provided by the organizers. The PPARR3 exercise consists of three stages, the first stage is a comparison of monthly global primary production fields generated by the different algorithms. Stage 2 is a step-by-step sensitivity study of the different algorithms tracking the derivation of sub-products in a series of point value estimates. The third stage is similar to PPARR1 and PPARR2 and is a blind comparison to the quality-controlled data base of carbon-14 measurements in the equatorial Pacific. We present here the results of the first stage, which compares the output of the models throughout an annual cycle, as well as two different years. Early results of the sensitivity analysis of Part 2 will also be shown.JRC.H.5-Rural, water and ecosystem resource

Trophic interactions within the Ross Sea continental shelf ecosystem

The continental shelf of the Ross Sea is one of the Antarctic's most intensively studied regions. We review the available data on the region's physical characteristics (currents and ice concentrations) and their spatial variations, as well as components of the neritic food web, including lower and middle levels (phytoplankton, zooplankton, krill, fishes), the upper trophic levels (seals, penguins, pelagic birds, whales) and benthic fauna. A hypothetical food web is presented. Biotic interactions, such as the role of Euphausia crystallorophias and Pleuragramma antarcticum as grazers of lower levels and food for higher trophic levels, are suggested as being critical. The neritic food web contrasts dramatically with others in the Antarctic that appear to be structured around the keystone species Euphausia superba. Similarly, we suggest that benthic–pelagic coupling is stronger in the Ross Sea than in most other Antarctic regions. We also highlight many of the unknowns within the food web, and discuss the impacts of a changing Ross Sea habitat on the ecosystem