Benthic foraminiferal response to changes in the northwestern Arabian Sea oxygen minimum zone (OMZ) during past $$\sim$$145 kyr

Abstract

The benthic foraminiferal abundance and diversity for the last *145 kyr at ODP Hole 723A in the northwestern Arabian Sea have been analyzed to better understand the factors responsible for the changes in the strength of Oxygen Minimum Zone (OMZ). The decline in the abundance of dysoxic taxa and more diverse fauna during interstadials of MIS 5 (5.5 and 5.1) along with higher percentages of G. bulloides reveal that the increased advection of well-oxygenated southern deep waters enhanced the rate of remineralization of sinking organic matter and also reduced the strength of OMZ. The improved supply of organic matter to the sea Coor due to southwest summer monsoon linked higher surface productivity between 114 and 108 ka and 102 and 92 ka enhanced the decay of organic matter utilizing more oxygen at intermediate depths which resulted in the development of strong OMZ. The increased inCow of well-oxygenated Sub-Antarctic Mode and Antarctic Intermediate Waters (SAMW-AAIW) and significantly reduced or negligible outCow of low oxygen Red Sea Water (RSW) in the northwestern Arabian Sea developed relatively weak OMZ and better bottom water oxygenation during early Holocene. The low abundance of G. bulloides indicates decline in the surface water productivity due to weaker southwest summer monsoon during late Holocene while more outCow of oxygen poor RSW at intermediate depths and no further inCow of well oxygenated SAMW-AAIW beyond 5°N relatively strengthens the OMZ in the northwestern Arabian Sea.

Distinct oxygenation modes of the Gulf of Oman during the past 43,000 years – a multi-proxy approach

“…Thus, phases with stronger SW monsoons, such as the D/O interstadials, are characterized by more input of low oxygen RSW and, therefore, sub-/anoxic conditions of bottom water in the Gulf of Oman. This corroborates findings from the Oman Upwelling area, where oxygen bottom water reconstructions using benthic foraminifera show oxygen depleted conditions during phases with higher outflow of RSW into the northwestern Arabian Sea (Pathak et al, 2021).…”

“…Bottom water oxygenation may not only be driven by processes in the upper water column but also by the occurrence of different water masses. The RSW is transported northward especially during the SW monsoon (Acharya and Panigrahi, 2016;Beal et al, 2000;Kumar and Prasad, 1999) and may undergo oxygen depletion due to higher organic matter supply and its decay on its way to the Gulf of Oman (Pathak et al, 2021). Acharya and Panigrahi (2016) have shown, that today's RSW core extends between 600 and 660 m reaching nearly the seafloor at the core site (~740 m).…”

Spatial and temporal variability of sea surface temperatures and monsoon dynamics in the northwestern Arabian Sea during the last 43 kyr

“…High saline PGW sinks below less-saline waters and produces a salinity maximum at depths between 200 to 400m (Bower and Furey, 2012;Pous et al, 2004;Prasad et al, 2001;Premchand et al, 1986;Shetye et al, 1994;Wyrtki, 1973). Similary, RSW is a warm, less oxygenated and high-saline water mass with an (Bower et al, 2000;Pathak et al, 2021;Rochford, 1964;Wyrtki, 1973).…”