Trends in summer bottom-water temperatures on the northern Gulf of Mexico continental shelf from 1985 to 2015

R Eugene Turner,Dubravko Justić,Nancy N Rabalais,João Miguel Dias

doi:10.1371/journal.pone.0184350

R Eugene Turner, Dubravko Justić + Show 2 more

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https://doi.org/10.1371/journal.pone.0184350

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Abstract

We quantified trends in the 1985 to 2015 summer bottom-water temperature on the northern Gulf of Mexico (nGOM) continental shelf for data collected at 88 stations with depths ranging from 3 to 63 m. The analysis was supplemented with monthly data collected from 1963 to 1965 in the same area. The seasonal summer peak in average bottom-water temperature varied concurrently with air temperature, but with a 2- to 5-month lag. The summer bottom-water temperature declined gradually with depth from 30 oC at stations closest to the shore, to 20 oC at the offshore edge of the study area, and increased an average 0.051 oC y-1 between1963 and 2015. The bottom-water warming in summer for all stations was 1.9 times faster compared to the rise in local summer air temperatures, and 6.4 times faster than the concurrent increase in annual global ocean sea surface temperatures. The annual rise in average summer bottom-water temperatures on the subtropical nGOM continental shelf is comparable to the few published temperature trend estimates from colder environments. These recent changes in the heat storage on the nGOM continental shelf will affect oxygen and carbon cycling, spatial distribution of fish and shrimp, and overall species diversity.

Highlights

The earth’s climate changed in various ways, amounts and intervals through geologic time, and recently from the added influence of changes in carbon storage on a planetary scale [1,2,3,4]
The Atchafalaya River plume remains in contact with the bottom for more than 15 km seaward of the river mouth [21], and westward flow occurs in the Louisiana Coastal Current (LCC) throughout most of the year [22]
The bottom-water temperature peaked in August at approx. 26 oC, when it was equal to the maximum air temperature, and fell to around 16 oC in January and February

Summary

Introduction

The earth’s climate changed in various ways, amounts and intervals through geologic time, and recently from the added influence of changes in carbon storage on a planetary scale [1,2,3,4]. The excess in global heat content is presently being stored mostly in the upper ocean (300 to 1000 m) [5,6]. Its distribution in the open ocean varies horizontally and vertically in response to currents, and to fluctuations in solar insolation, clouds, and various atmospheric factors, among others, that are regionally diverse [1]. The direct and long-term quantification of global temperature changes on continental shelves is not well-represented in the scientific literature because of, for example, their small area relative to the open ocean, insufficient monitoring efforts, and/or funding limitations.

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