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Low-oxygen “dead zone” in the northern Gulf of Mexico predicted to grow to 12,600
km2 this summer (HALIFAX, N.S.) Monday, June 5, 2023 – Dalhousie University scientists
forecast that the size of the hypoxic zone (also known as “dead zone”) in the
northern Gulf of Mexico will reach 9,200 km2 by 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 12,600 km2 by the end of
August. This maximum is more than twice size of Prince Edward Island and smaller
by 10% than the 36-year average Gulf hypoxic zone of 13,900 km2. The Dalhousie
forecast is part of the annual ensemble 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 similar to 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 6th year that a forecast with this level of detail has
been produced (see 2018 forecast here, 2019 forecast here, 2020 forecast here, 2021 forecast here, and the 2022 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 for July 29, 2023. The
black line delimits the most probable region of hypoxic conditions.
Figure 2: Predicted temporal
evolution of the hypoxic zone in 2022 shown by the black line. Grey shading
indicates the 95% confidence interval, a measure of forecast uncertainty. The
red dot marks July 29, 2023. 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) |
