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Benthic Biogeochemical Processes Rel...

LeMieux, Sydnie Lynn.

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Benthic Biogeochemical Processes Related to Water Column Oxygen Deficiency in the Santa Monica Basin, North East Pacific Ocean.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Benthic Biogeochemical Processes Related to Water Column Oxygen Deficiency in the Santa Monica Basin, North East Pacific Ocean./
Author:	LeMieux, Sydnie Lynn.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2017,
Description:	88 p.
Notes:	Source: Masters Abstracts International, Volume: 57-02.
Contained By:	Masters Abstracts International57-02(E).
Subject:	Biogeochemistry. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10688092
ISBN:	9780355534528

Benthic Biogeochemical Processes Related to Water Column Oxygen Deficiency in the Santa Monica Basin, North East Pacific Ocean.
LeMieux, Sydnie Lynn.

Benthic Biogeochemical Processes Related to Water Column Oxygen Deficiency in the Santa Monica Basin, North East Pacific Ocean. - Ann Arbor : ProQuest Dissertations & Theses, 2017 - 88 p.

Source: Masters Abstracts International, Volume: 57-02.

Thesis (M.S.)--University of California, Los Angeles, 2017.

Mid-water oceanic depths in coastal upwelling regions often contain oxygen deficient waters, called oxygen minimum zones (OMZs). These hypoxic (< 60 microM O2) conditions can have adverse effects on ecosystems, as many organisms cannot survive in low O2 conditions. This study investigated the OMZ in the topographically isolated Santa Monica Basin (SMB), California, a recipient of high nutrient input. The last survey of this area ~35 years ago, reported a pervious 350 year expansion of the SMB OMZ. In order to assess the OMZ since the last evaluation, sediment cores from 12 stations were retrieved by a multicorer from O2-ventilated (>60 muM O2) to near-anoxia (~4 muM O2) regions along two depth-transects ranging from water depths between 71 and 907 m. The sediment porewater and supernatant water of the cores were analyzed for sulfate (SO42-), nitrate (NO3 -), phosphate (PO43-), ammonium (NH 4+), total sulfide, dissolved iron (Fe (II)), total alkalinity (TA) and bacterial sulfate reduction. The two deepest stations (907 and 893 meters, ~5 microM O2) exhibited down-core accumulation of NH 4+ and TA, while also displaying enhanced rates of sulfate reduction close to the sediment surface; these patterns are all evidence of low oxygen conditions in the overlying water column. Shallower stations upslope (starting at 777 m water depth) featured increasing signs of bioturbation and bioirrigation effects in the geochemical profiles of NH4 +, TA, PO43- and Fe (II). Low sulfate reduction rates (areal rates range from 0.13--0.86 mmol m-2 d -1) were detected at all stations. These results were compared with data separate from this thesis, including: 210Pb lamination analyses, the presence and activity of macrofauna at the seafloor, and iron speciation analyses. According to the stations sampled, we could not identify a definite spreading or reduction of the OMZ at the seafloor since the last survey of the SMB was done ~35 years ago.

ISBN: 9780355534528Subjects--Topical Terms:

545717
Biogeochemistry.

Benthic Biogeochemical Processes Related to Water Column Oxygen Deficiency in the Santa Monica Basin, North East Pacific Ocean.
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520 $a Mid-water oceanic depths in coastal upwelling regions often contain oxygen deficient waters, called oxygen minimum zones (OMZs). These hypoxic (< 60 microM O2) conditions can have adverse effects on ecosystems, as many organisms cannot survive in low O2 conditions. This study investigated the OMZ in the topographically isolated Santa Monica Basin (SMB), California, a recipient of high nutrient input. The last survey of this area ~35 years ago, reported a pervious 350 year expansion of the SMB OMZ. In order to assess the OMZ since the last evaluation, sediment cores from 12 stations were retrieved by a multicorer from O2-ventilated (>60 muM O2) to near-anoxia (~4 muM O2) regions along two depth-transects ranging from water depths between 71 and 907 m. The sediment porewater and supernatant water of the cores were analyzed for sulfate (SO42-), nitrate (NO3 -), phosphate (PO43-), ammonium (NH 4+), total sulfide, dissolved iron (Fe (II)), total alkalinity (TA) and bacterial sulfate reduction. The two deepest stations (907 and 893 meters, ~5 microM O2) exhibited down-core accumulation of NH 4+ and TA, while also displaying enhanced rates of sulfate reduction close to the sediment surface; these patterns are all evidence of low oxygen conditions in the overlying water column. Shallower stations upslope (starting at 777 m water depth) featured increasing signs of bioturbation and bioirrigation effects in the geochemical profiles of NH4 +, TA, PO43- and Fe (II). Low sulfate reduction rates (areal rates range from 0.13--0.86 mmol m-2 d -1) were detected at all stations. These results were compared with data separate from this thesis, including: 210Pb lamination analyses, the presence and activity of macrofauna at the seafloor, and iron speciation analyses. According to the stations sampled, we could not identify a definite spreading or reduction of the OMZ at the seafloor since the last survey of the SMB was done ~35 years ago.
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