Journal: Journal of Geophysical Research: Oceans

Abbreviation

J. geophys. res. Ocean.

Publisher

Wiley

Journal Volumes

ISSN

0148-0227
2169-9275

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2018 - 201932020 - 20244
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Publications 1 - 7 of 7
  • Radium Isotopes Across the Arctic Ocean Show Time Scales of Water Mass Ventilation and Increasing Shelf Inputs
    Item type: Journal Article
    Rutgers van der Loeff, Michiel; Kipp, Lauren; Charette, Matthew A.; et al. (2018)
    Journal of Geophysical Research: Oceans
    The first full transarctic section of 228Ra in surface waters measured during GEOTRACES cruises PS94 and HLY1502 (2015) shows a consistent distribution with maximum activities in the transpolar drift. Activities in the central Arctic have increased from 2007 through 2011 to 2015. The increased 228Ra input is attributed to stronger wave action on shelves resulting from a longer ice‐free season. A concomitant decrease in the 228Th/228Ra ratio likely results from more rapid transit of surface waters depleted in 228Th by scavenging over the shelf. The 228Ra activities observed in intermediate waters (<1,500 m) in the Amundsen Basin are explained by ventilation with shelf water on a time scale of about 15–18 years, in good agreement with estimates based on SF6 and 129I/236U. The 228Th excess below the mixed layer up to 1,500 m depth can complement 234Th and 210Po as tracers of export production, after correction for the inherent excess resulting from the similarity of 228Ra and 228Th decay times. We show with a Th/Ra profile model that the 228Th/228Ra ratio below 1,500 m is inappropriate for this purpose because it is a delicate balance between horizontal supply of 228Ra and vertical flux of particulate 228Th. The accumulation of 226Ra in the deep Makarov Basin is not associated with an accumulation of Ba and can therefore be attributed to supply from decay of 230Th in the bottom sediment. We estimate a ventilation time of 480 years for the deep Makarov‐Canada Basin, in good agreement with previous estimates using other tracers.
  • Holocene Palaeoenvironmental and Palaeoproductivity Changes in the Western Amundsen Sea Embayment of Antarctica
    Item type: Journal Article
    Kim, Minkyoung; Lee, Jae Il; Bak, Young-Suk; et al. (2023)
    Journal of Geophysical Research: Oceans
    The Amundsen Polynya (AP) on the inner and middle continental shelf of the western Amundsen Sea Embayment is the fourth largest coastal polynya around Antarctica. The AP is highly productive when it opens in austral summer, with similar to 20 times greater organic carbon accumulation rates over the last few thousand years compared to those at nearby shelf sites with more persistent seasonal sea-ice cover. We examined sedimentary records at a site from the AP and another site from the outer shelf to investigate temporal variations in the depositional environment with a special focus on the timing of the AP opening since the deglaciation following the Last Glacial Maximum (LGM; ca. 23-19 cal. ka BP). In the AP region, sedimentological and biogeochemical proxy data reveal a transition from a sub-glacial to a sub-ice shelf and then seasonally open marine conditions comparable to those at present. Total organic carbon contents and diatom valve abundances during the seasonally open marine period imply that the polynya environments was reached at ca. 9.2 cal. ka BP. Since the post-LGM deglaciation, diatom productivity and assemblages in the AP region appear to have varied in association with the variation in the physical environment. Compared to the AP site, only small amounts of organic carbon accumulated on the outer shelf. Differences in the depositional environments and productivity modes between the inner and outer shelf sites have persisted since ca. 10.5 cal. ka BP.
  • Anthropogenic Carbon in the Arctic Ocean: Perspectives From Different Transient Tracers
    Item type: Journal Article
    Raimondi, Lorenza; Wefing, Anne-Marie; Casacuberta, Núria (2024)
    Journal of Geophysical Research: Oceans
    In this study we investigated the physical characteristics of the Atlantic layer in the Arctic Ocean (AO) and its role in the distribution and storage of anthropogenic carbon (Cant). The novelty of this work is to use the Transit Time Distribution method (TTD) with the radionuclides 129I and 236U and its comparison to the commonly applied gas tracers, CFC-12 and SF6. Overall, our examination of two distinct tracer pairs, along with the novel TTD method in comparison to a classical approach, revealed a notable agreement, highlighting the robustness of these Cant estimates. The TTD analysis based on radionuclides showed that whereas the Eurasian Basin has shorter transit times and is dominated by strong mixing conditions, the Amerasian Basin is characterized by longer transit times and a strong advective flow. Overall, the Cant concentrations obtained from radionuclides confirm that the distribution in the AO follows its circulation patterns, with higher concentrations in the Eurasian Basin (∼50 μmol kg−1) compared to the Amerasian one (∼36–42 μmol kg−1). An estimated partial inventory of 0.85 ± 0.17 and 1.0 ± 0.03 Pg C was assessed for 2015 from the novel application of TTD with radionuclides and gas tracers, respectively. Finally, we identified the saturation of gas tracers as a larger source of uncertainty for Cant estimation compared to the uncertainty associated to different radionuclides' input functions, thus remarking the importance of including non-saturation dependent tracers, such as radionuclides, as an additional tool to support Cant estimates in the AO.
  • Hydrogen Isotope Fingerprinting of Lipid Biomarkers in the Chinese Marginal Seas
    Item type: Journal Article
    Li, Li; Sachs, Julian P.; Yu, Meng; et al. (2024)
    Journal of Geophysical Research: Oceans
  • Circulation Timescales and Pathways of Atlantic Water in the Canada Basin: Insights From Transient Tracers ¹²⁹I and ²³⁶U
    Item type: Journal Article
    Payne, Annabel; Wefing, Anne-Marie; Christl, Marcus; et al. (2024)
    Journal of Geophysical Research: Oceans
    Anthropogenic radionuclides 129I and 236U are used to investigate pathways of the Atlantic Water flow in the Canada Basin, estimate transport timescales, and investigate mixing dynamics within the Atlantic Water layer and the overlying Pacific Water. Transit Time Distribution (TTD) model mean ages indicate water takes 25–35 years to reach the Canada Basin from the entrance of the Arctic, with limited lateral and vertical mixing along the core of the Arctic Ocean Boundary Current. Mode ages obtained from the model yield shorter transport times of 20–32 years. These age estimates agree with previous studies using these radionuclides and ventilation tracers in this region, indicating a steady-state flow of Atlantic Water for the last 15 years. The distribution of the isotopes in the Atlantic layer indicates two pathways Atlantic Water may take into the basin, supported by the distribution of ages in the TTD model. End-member mixing models indicate that the Pacific Winter water acquires a 20%–40% Atlantic Water signal of the radionuclides, upwelled over short periods, most likely along the shelf and Barrow Canyon region.
  • Tracing Atlantic Waters Using 129I and 236U in the Fram Strait in 2016
    Item type: Journal Article
    Wefing, Anne-Marie; Christl, Marcus; Vockenhuber, Christof; et al. (2019)
    Journal of Geophysical Research: Oceans
  • Contrasting Impact of Future CO2 Emission Scenarios on the Extent of CaCO3 Mineral Undersaturation in the Humboldt Current System
    Item type: Journal Article
    Franco, Ana C.; Gruber, Nicolas; Frölicher, Thomas L.; et al. (2018)
    Journal of Geophysical Research: Oceans
Publications 1 - 7 of 7