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Low-oxygen
“dead zone” in the northern Gulf of Mexico predicted to grow to 19,000 km2
this summer (HALIFAX, N.S.)
Wednesday, June 3, 2020 – Dalhousie University scientists forecast that the
size of the hypoxic zone (also known as “dead zone”) in the northern the Gulf
of Mexico will reach 19,000 km2 at the end of July, when an
annually recurring monitoring cruise typically maps location and extent of
the hypoxic zone, and will grow to a maximum extent of 22,000 km2
in early August. This maximum is almost four times the size of Prince Edward
Island and much bigger than the 33-year average Gulf hypoxic zone of 14,000
km2. The Dalhousie forecast is part of the annual
dead-zone forecast by the National Oceanic and Atmospheric
Administration (NOAA) and the United States Geological Survey (USGS). NOAA
and USGS forecast a size of 17,000 km2 for late July, which is the
average forecast of an ensemble of six statistical models, including the
Dalhousie forecast. The hypoxic
zone in the northern Gulf of Mexico forms every summer and is the largest in
North American coastal waters. Freshwater and plant nutrients—mostly from
unused agricultural fertilizer, and urban and industrial wastewater—travel to
the Gulf via the Mississippi River. These nutrients stimulate a sequence of
biological transformations in coastal waters that significantly decrease oxygen
levels near the bottom resulting in an environment unable to support most
higher marine life forms. All forecasts
of the hypoxic zone in the northern Gulf of Mexico are based on an estimate
of spring nutrient discharge from the Mississippi, determined by the USGS in
the first week of June. The forecast model developed by Dalhousie scientists
Arnaud Laurent and Katja Fennel is unique in its ability to provide a
temporally and spatially explicit forecast, in other words, the hypoxic
zone’s location, size and evolution is predicted throughout the summer season.
This is the 3rd year that a forecast with this level of detail has been produced
(see 2018 forecast here and 2019 forecast here). Many other coastal regions around the globe are experiencing
declines in oxygen, leaving marine animals increasingly gasping for breath.
In the Canadian Maritimes, the Gulf of St. Lawrence and the Scotian Shelf are
suffering from low-oxygen in near-bottom waters, squeezing the habitat of several commercially important and
endangered fish species. This trend has been ongoing for several decades, as man-made
inputs of nutrients and global warming conspire to depress oxygen levels in
coastal ocean waters. Contacts Dr. Katja
Fennel, Killam Professor Department of
Oceanography Dalhousie
University Tel: +1 902
494 4526 Email: katja.fennel@dal.ca Dr. Arnaud
Laurent, Research Associate Department of
Oceanography Dalhousie
University Email: arnaud.laurent@dal.ca Additional
Information
Figure 1: Predicted probability of hypoxic conditions
in the northern Gulf of Mexico on July 28, 2020. The black line delimits the
most probable region of hypoxic conditions.
Figure 2: Predicted temporal evolution of the
hypoxic zone in 2019 shown by the black line. Grey shading indicates the 95%
confidence interval, a measure of forecast uncertainty. The red dots marks
July 28, 2020. Animation of the temporal evolution of the
forecast hypoxic area in the northern Gulf of Mexico: here Related Materials: Fennel, K., and
Testa, J.M., Biogeochemical controls on coastal
hypoxia, Annual
Review of Marine Science, 11, 105-130 (2019) Laurent, A.,
Fennel, K., Time-evolving, spatially explicit
forecasts of the northern Gulf of Mexico hypoxic zone, Environmental Science &
Technology, 53, 14,449-14,458, doi:
10.1021/acs.est.9b05790 (2019) Model code freely available at https://www.mathworks.com/matlabcentral/fileexchange/73445-laurentfennel2019_est Laurent, A., Fennel,
K., Ko, D.S., Lehrter J., Climate change projected
to exacerbate impacts of coastal eutrophication in the northern Gulf of
Mexico, Journal of Geophysical Research-Oceans,
123, doi:
10.1002/2017JC013583 (2018) Fennel, K.
and Laurent, A., N
and P as ultimate and proximate limiting nutrients in the northern Gulf of
Mexico: implications for hypoxia reduction strategies, Biogeosciences, 15, 3121-3131 (2018) Brennan,
C.E., H. Blanchard and K. Fennel, Putting
Temperature and Oxygen Thresholds of Marine Animals in Context of
Environmental Change: A Regional Perspective for the Scotian Shelf and Gulf
of St. Lawrence, PLOS ONE, 11(12) e0167411.doi:10.1371/journal.pone.0167411 (2016) Bianucci, L.,
Fennel, K., Chabot, D., Shackell, N., Lavoie, D., Ocean
biogeochemical models as management tools: a case study for Atlantic wolffish and declining oxygen, ICES
Journal of Marine Science, 73(2):263-274,
doi: 10.1093/icesjms/fsv220
(2016) |
