TY - JOUR
T1 - Recent expansion and intensification of hypoxia in the Arabian Gulf and its drivers
AU - Lachkar, Zouhair
AU - Mehari, Michael
AU - Lévy, Marina
AU - Paparella, Francesco
AU - Burt, John A.
N1 - Funding Information:
Support for this research has come from the Arabian Center for Climate and Environmental Sciences (ACCESS), through the New York University Abu Dhabi (NYUAD) Research Institute Grant CG009. JB and FP were supported by Tamkeen through research grant GC009 to the Arabian Center for Climate and Environmental Sciences and, respectively, research grant CG007 to the NYUAD Water Research Center and research grant CG002 to the NYUAD SITE Research Center; their support is greatly appreciated.
Publisher Copyright:
Copyright © 2022 Lachkar, Mehari, Lévy, Paparella and Burt.
PY - 2022/9/7
Y1 - 2022/9/7
N2 - The Arabian Gulf (also known as Persian Gulf, hereafter Gulf) is a shallow semi-enclosed subtropical sea known for its extreme physical environment. Recent observations suggest a decline in oxygen concentrations in the Gulf over the past few decades accompanied by an expansion of seasonal near-bottom hypoxia. Here, we reconstruct the evolution of dissolved oxygen in the Gulf from 1982 through 2010 and explore its controlling factors. To this end, we use an eddy-resolving hindcast simulation forced with winds and heat and freshwater fluxes from an atmospheric reanalysis. We show that seasonal near-bottom hypoxia (O2< 60 mmol m-3) emerges in the deeper part of the Gulf over summer and peaks in autumn in response to enhanced vertical stratification inhibiting mixing and O2 replenishment at depth. We also find a significant deoxygenation in the Gulf over the study period, with the Gulf O2 content dropping by nearly 1% per decade and near-bottom O2 decreasing by between 10 and 30 mmol m-3 in the deeper part of the Gulf between the early 1980s and the late 2000s. These changes result in the horizontal expansion of seasonal bottom hypoxia with the hypoxia-prone seafloor area increasing from less than 20,000 km2 in the 1980s to around 30,000 km2 in the 2000s. The expansion of hypoxia is also accompanied by a lengthening of the hypoxic season with hypoxia emerging locally 1 to 2 months earlier in the late 2000s relative to the early 1980s. Furthermore, declining near-bottom O2 levels result in the expansion of suboxic conditions (O2< 4 mmol m-3) and the emergence and amplification of denitrification there. An analysis of the Gulf oxygen budget demonstrates that deoxygenation is essentially caused by reduced oxygen solubility near the surface and enhanced respiration near the bottom. While reduced solubility results from the warming of the Gulf waters, enhanced respiration is mostly driven by an increased supply of nutrients imported from the Arabian Sea due to the weakening of winter Shamal winds over the study period. Our findings suggest that recent changes in local climate are not only altering the Gulf physical environment but are also having a strong impact on the Gulf biogeochemistry with profound potential implications for the ecosystems and the fisheries of the region.
AB - The Arabian Gulf (also known as Persian Gulf, hereafter Gulf) is a shallow semi-enclosed subtropical sea known for its extreme physical environment. Recent observations suggest a decline in oxygen concentrations in the Gulf over the past few decades accompanied by an expansion of seasonal near-bottom hypoxia. Here, we reconstruct the evolution of dissolved oxygen in the Gulf from 1982 through 2010 and explore its controlling factors. To this end, we use an eddy-resolving hindcast simulation forced with winds and heat and freshwater fluxes from an atmospheric reanalysis. We show that seasonal near-bottom hypoxia (O2< 60 mmol m-3) emerges in the deeper part of the Gulf over summer and peaks in autumn in response to enhanced vertical stratification inhibiting mixing and O2 replenishment at depth. We also find a significant deoxygenation in the Gulf over the study period, with the Gulf O2 content dropping by nearly 1% per decade and near-bottom O2 decreasing by between 10 and 30 mmol m-3 in the deeper part of the Gulf between the early 1980s and the late 2000s. These changes result in the horizontal expansion of seasonal bottom hypoxia with the hypoxia-prone seafloor area increasing from less than 20,000 km2 in the 1980s to around 30,000 km2 in the 2000s. The expansion of hypoxia is also accompanied by a lengthening of the hypoxic season with hypoxia emerging locally 1 to 2 months earlier in the late 2000s relative to the early 1980s. Furthermore, declining near-bottom O2 levels result in the expansion of suboxic conditions (O2< 4 mmol m-3) and the emergence and amplification of denitrification there. An analysis of the Gulf oxygen budget demonstrates that deoxygenation is essentially caused by reduced oxygen solubility near the surface and enhanced respiration near the bottom. While reduced solubility results from the warming of the Gulf waters, enhanced respiration is mostly driven by an increased supply of nutrients imported from the Arabian Sea due to the weakening of winter Shamal winds over the study period. Our findings suggest that recent changes in local climate are not only altering the Gulf physical environment but are also having a strong impact on the Gulf biogeochemistry with profound potential implications for the ecosystems and the fisheries of the region.
KW - Arabian (Persian) Gulf
KW - climate change
KW - marine biogeochemical ecosystem model
KW - marine hypoxia
KW - ocean deoxygenation
KW - ocean warming
KW - semi-enclosed seas
UR - http://www.scopus.com/inward/record.url?scp=85138554266&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85138554266&partnerID=8YFLogxK
U2 - 10.3389/fmars.2022.891378
DO - 10.3389/fmars.2022.891378
M3 - Article
AN - SCOPUS:85138554266
SN - 2296-7745
VL - 9
JO - Frontiers in Marine Science
JF - Frontiers in Marine Science
M1 - 891378
ER -