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Low-oxygen “dead zone” in the northern
Gulf of Mexico predicted to grow to 26,000 km2 this summer (HALIFAX, N.S.)
Thursday, June 10, 2019 – 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 22,000 km2 at the end of July, when a
monitoring cruise will map location and extent of the hypoxic zone, and will grow
to a maximum extent of 26,000 km2 in early August. This maximum is
over four-and-a-half 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 20,000 km2 for late July, which is the
average of an ensemble of five statistical models.
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 only the 2nd year that a forecast with this level of detail has been produced
(see 2018 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 27, 2019. The thick black line delimits
the most probable location of the hypoxic area.
Figure 2: Predicted temporal evolution of the
hypoxic zone in 2019 shown by the black line. Grey shading indicates the
uncertainty. 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., 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) |
