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Low-oxygen
“dead zone” in the northern Gulf of Mexico predicted to grow to 11,400 km2
this summer (HALIFAX, N.S.)
Thursday, June 3, 2021 – Dalhousie University scientists forecast that the
size of the hypoxic zone (also known as “dead zone”) in the northern Gulf of
Mexico will reach 11,400 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 14,700 km2 in early
August. This maximum is almost three times the size of Prince Edward Island
and similar to 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). The NOAA
and USGS forecast, which is the average of an ensemble of six statistical models
including the Dalhousie model, is 12,600 km2. 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 4th year that a forecast with this level of detail has
been produced (see 2018 forecast here, 2019 forecast here,
and 2020 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 29, 2021. The black line delimits the
most probable region of hypoxic conditions.
Figure 2: Predicted temporal evolution of the
hypoxic zone in 2021 shown by the black line. Grey shading indicates the 95%
confidence interval, a measure of forecast uncertainty. The red dot marks
July 29, 2021. 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) |
