Sohm Jill A.

No Thumbnail Available
Last Name
Sohm
First Name
Jill A.
ORCID

Filters

1 1
2011 - 2019 1 2020 - 2022 1
2
2
Reset filters

Settings

Search Results

Now showing 1 - 2 of 2
  • Article
    Nitrogen fixation in the South Atlantic Gyre and the Benguela Upwelling System
    (American Geophysical Union, 2011-08-27) Sohm, Jill A. ; Hilton, Jason A. ; Noble, Abigail E. ; Zehr, Jonathan P. ; Saito, Mak A. ; Webb, Eric A.
    Dinitrogen (N2) fixation is recognized as an important input of new nitrogen (N) to the open ocean gyres, contributing to the export of organic matter from surface waters. However, very little N2-fixation research has focused on the South Atlantic Gyre, where dust deposition of iron (Fe), an important micronutrient for diazotrophs, is seasonally low. Recent modeling efforts suggest that N2-fixation may in fact be closely coupled to, and greatest in, areas of denitrification, as opposed to the oceanic gyres. One of these areas, the Benguela Upwelling System, lies to the east of the South Atlantic Gyre. In this study we show that N2-fixation in surface waters across the South Atlantic Gyre was low overall (<1.5 nmol N l−1 d−1) with highest rates seen in or near the Benguela Upwelling System (up to ∼8 nmol N l−1 d−1). Surface water dissolved Fe (dFe) concentrations were very low in the gyre (∼0.3 nM or lower), while soluble reactive phosphorus (SRP) concentrations were relatively high (∼0.15 μM). N2-fixation rates across the entire sampling area were significantly positively correlated to dFe, but also to SRP and NO3−. Thus, high NO3− concentrations did not exclude N2-fixation in the upwelling region, which provides evidence that N2-fixation may be occurring in previously unrecognized waters, specifically near denitrification zones. However the gene encoding for a nitrogenase component (nifH) was not detected from known diazotrophs at some stations in or near the upwelling where N2-fixation was greatest, suggesting the presence of unknown diazotrophs in these waters.
  • Article
    A global ocean dissolved organic phosphorus concentration database (DOPv2021)
    (Nature Research, 2022-12-16) Liang, Zhou ; McCabe, Kelly ; Fawcett, Sarah E. ; Forrer, Heather J. ; Hashihama, Fuminori ; Jeandel, Catherine ; Marconi, Dario ; Planquette, Hélène ; Saito, Mak A. ; Sohm, Jill A. ; Thomas, Rachel K. ; Letscher, Robert T. ; Knapp, Angela N.
    Dissolved organic phosphorus (DOP) concentration distributions in the global surface ocean inform our understanding of marine biogeochemical processes such as nitrogen fixation and primary production. The spatial distribution of DOP concentrations in the surface ocean reflect production by primary producers and consumption as an organic nutrient by phytoplankton including diazotrophs and other microbes, as well as other loss processes such as photolysis. Compared to dissolved organic carbon and nitrogen, however, relatively few marine DOP concentration measurements have been made, largely due to the lack of automated analysis techniques. Here we present a database of marine DOP concentration measurements (DOPv2021) that includes new (n = 730) and previously published (n = 3140) observations made over the last ~30 years (1990-2021), including 1751 observations in the upper 50 m. This dataset encompasses observations from all major ocean basins including the poorly represented Indian, South Pacific, and Southern Oceans and provides insight into spatial distributions of DOP in the ocean. It is also valuable for researchers who work on marine primary production and nitrogen fixation.