07 May 2019
 | 07 May 2019
Status: this discussion paper is a preprint. It has been under review for the journal Biogeosciences (BG). The manuscript was not accepted for further review after discussion.

Ventilation dynamics of the Oxygen Minimum Zone in the Arabian Sea

Henrike Schmidt, Rena Czeschel, and Martin Visbeck

Abstract. Oxygen minimum zones (OMZs) in the open ocean occur below the surface in regions of weak ventilation and high biological productivity. Very low levels of dissolved oxygen affect marine life and alter biogeochemical cycles. One of the most intense but least understood OMZs in the world is located in the Arabian Sea in a depth range between 300 to 1000 m. Within the last decades observations suggest a decreasing oxygen trend. Thus, an improved understanding of the crucial processes is necessary for a reliable assessment of the future development of the Arabian Sea OMZ.

This study uses a combination of observational data as well as reanalysis velocity fields from the ocean model Hycom (Hybrid Coordinate Ocean Model) to explore the ventilation dynamics of the Arabian Sea OMZ. Our results show that the OMZ features a strong seasonal cycle with regional differences that is correlated with the monsoon system:

In the eastern basin, the OMZ is strongest during the winter monsoon with a core thickness of 1000 m depth and oxygen values of less than 5 µmol/kg. Ventilation during that phase is dominated by Persian Gulf water, that clockwise circles the perimeter of the basin and enters the OMZ from the north. During the summer monsoon ventilation from the southeast leads to higher oxygen values indicating a reverse flow along the Indian coast in the intermediate layer compared to the southeastward surface currents.

The seasonal cycle in the western basin has the same seasonality as the one in the eastern basin with a core thickness of 900 m during the winter monsoon. The oxygen supply during the summer monsoon is weaker compared to the eastern basin and correlates with the ventilation of Persian Gulf (Red Sea) water during the summer monsoon (autumn inter-monsoon) phase. As the interior exchange between the eastern and western basin is weak, the more pronounced OMZ in the eastern basin is explained by prolonged ventilation time scales. For the eastern (western) basin Persian Gulf water needs 2–3 (1–2) years and Red Sea water 7–8 (3–4) years to ventilate the OMZ.

Henrike Schmidt, Rena Czeschel, and Martin Visbeck
Henrike Schmidt, Rena Czeschel, and Martin Visbeck
Henrike Schmidt, Rena Czeschel, and Martin Visbeck


Total article views: 1,803 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
1,201 550 52 1,803 145 48 54
  • HTML: 1,201
  • PDF: 550
  • XML: 52
  • Total: 1,803
  • Supplement: 145
  • BibTeX: 48
  • EndNote: 54
Views and downloads (calculated since 07 May 2019)
Cumulative views and downloads (calculated since 07 May 2019)

Viewed (geographical distribution)

Total article views: 1,637 (including HTML, PDF, and XML) Thereof 1,633 with geography defined and 4 with unknown origin.
Country # Views %
  • 1


Latest update: 18 Apr 2024
Short summary
Our investigations give a detailed insight on the changing current system at intermediate depth in the Arabian Sea and allow to draw conclusions on ventilation pathways of the oxygen minimum zone and its seasonal variability. In response to the monsoon system the boundary currents change direction and feature a regionally varying ventilation pattern.