Response of export production and dissolved oxygen concentrations in oxygen minimum zones to &amp;lt;i&amp;gt;p&amp;lt;/i&amp;gt;CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and temperature stabilization scenarios in the biogeochemical model HAMOCC 2.0

Teresa Beaty,Arne M E Winguth,Taylor Hughlett,Christoph Heinze

doi:10.5194/bg-14-781-2017

Abstract

Abstract. Dissolved oxygen (DO) concentration in the ocean is an important component of marine biogeochemical cycles and will be greatly altered as climate change persists. In this study a global oceanic carbon cycle model (HAMOCC 2.0) is used to address how mechanisms of oxygen minimum zone (OMZ) expansion respond to changes in CO2 radiative forcing. Atmospheric pCO2 is increased at a rate of 1 % annually and the model is stabilized at 2 ×, 4 ×, 6 ×, and 8 × preindustrial pCO2 levels. With an increase in CO2 radiative forcing, the OMZ in the Pacific Ocean is controlled largely by changes in particulate organic carbon (POC) export, resulting in increased remineralization and thus expanding the OMZs within the tropical Pacific Ocean. A potential decline in primary producers in the future as a result of environmental stress due to ocean warming and acidification could lead to a substantial reduction in POC export production, vertical POC flux, and thus increased DO concentration particularly in the Pacific Ocean at a depth of 600–800 m. In contrast, the vertical expansion of the OMZs within the Atlantic is linked to increases POC flux as well as changes in oxygen solubility with increasing seawater temperature. Changes in total organic carbon and increase sea surface temperature (SST) also lead to the formation of a new OMZ in the western subtropical Pacific Ocean. The development of the new OMZ results in dissolved oxygen concentration of ≤ 50 µmol kg−1 throughout the equatorial Pacific Ocean at 4 times preindustrial pCO2. Total ocean volume with dissolved oxygen concentrations of ≤ 50 µmol kg−1 increases by 2.4, 5.0, and 10.5 % for the 2 ×, 4 ×, and 8 × CO2 simulations, respectively.

Highlights

Rapid increases in concentrations of greenhouse gases (CO2, CH4, and N2O) in the atmosphere since the 18th century have led to greenhouse gas radiative forcing and temperature change of 0.068 ◦C per decade (Karl et al, 2015)
production of POC (PPOC) is decreasing as expected with the reduction in ventilation, DOC increase with a loss of 25 and 50 %, leading to the expansion of the oxygen minimum zone (OMZ) in these two simulations
Understanding the extent and the mechanisms for these OMZ expansions and how models respond to changes in expansion mechanism is of the utmost importance in order to more accurately predict environmental changes in these regions

Summary

Introduction

Rapid increases in concentrations of greenhouse gases (CO2, CH4, and N2O) in the atmosphere since the 18th century have led to greenhouse gas radiative forcing and temperature change of 0.068 ◦C per decade (Karl et al, 2015). A rise in ocean temperature decreases the solubility of CO2 in seawater and the CO2 uptake into the ocean. The ocean buffer capacity decreases with rising pCO2. Changes in climate as a result of CO2 emission will affect the oxygen distribution in the ocean. DO (dissolved oxygen) concentration in the ocean is affected by changes in ocean ventilation and by solubility and the biological pump (Volk and Hoffert, 1985).

Methods

Results

Discussion

Conclusion