Increase in marine heat waves threatens coastal habitats
With continued warming, Chesapeake Bay will suffer extreme heat for half
the year by 2100

Date:
January 18, 2022
Source:
Virginia Institute of Marine Science
Summary:
Heat waves -- like the one that blistered the Pacific Northwest
last June -- also occur underwater. A new study paints a worrisome
picture of recent and projected trends in marine heat waves within
the nation's largest estuary, with dire implications for the marine
life and coastal economy of the Chesapeake Bay and other similarly
impacted shallow-water ecosystems.



FULL STORY ==========================================================================
Heat waves -- like the one that blistered the Pacific Northwest last June
- - also occur underwater. A new study in Frontiers in Marine Science
paints a worrisome picture of recent and projected trends in marine
heat waves within the nation's largest estuary, with dire implications
for the marine life and coastal economy of the Chesapeake Bay and other similarly impacted shallow- water ecosystems.


==========================================================================
The study's authors, Drs. Piero Mazzini and Cassia Pianca of William &
Mary's Virginia Institute of Marine Science, note they saw "significant
upward trends in the frequency and yearly cumulative intensity of marine
heat waves within the Chesapeake Bay." The pair based their analysis
on long-term measurements of water temperature from 6 sites along the
Bay's 200-mile length, with record length varying between 26 and 35
years. Like other researchers, they defined a marine heat wave as any
period of 5 or more consecutive days with water temperatures warmer than
90% of those measured on the same date and in the same spot as in years
past. They analyzed the record of Bay heat waves in terms of frequency, intensity, duration, and cumulative temperature stress.

Based on those criteria, Mazzini and Pianca determined that the Chesapeake
Bay experienced an average of two 11-day marine heat waves per year
between 1986 and 2020, with an average intensity of 5.4 DEGF (3 DEGC)
and a maximum peak of 14.4 DEGF (8 DEGC) above the climatic norm. This translates to an average yearly cumulative intensity of 130 DEGF (72
DEGC) days, a measure of heat stress for marine systems similar to the
"cooling degree days" used to determine the energy required to keep
indoor spaces comfortable for people.

The researcher's most troubling finding was that the maximum frequency
of marine heat waves occurred during the last 10 years, reaching 6-8
events per year compared to only 4-5 events per year prior to 2010. That
equals a gain of 1.4 annual heat waves each decade, with a corresponding increase in annual cumulative intensity. The researchers also found that
years without marine heat waves were fairly common in Bay waters prior
to 2010, but have occurred baywide only once since, in 2014.

"If these trends persist," says Mazzini, "the Bay will experience heat
waves on a monthly basis within the next 50 years, and by the end of
the century will reach a semi-permanent heat-wave state, with extreme temperatures present for more than half the year." The authors warn
this would have devastating impacts on the Bay ecosystem, aggravating
the effects of nutrient pollution, increasing the severity of low-
oxygen "dead-zones," stimulating algal blooms, stressing or killing
bottom- dwelling communities, causing shifts in species composition,
and leading to declines in important commercial fishery species such as
striped bass. Similar trends and impacts are likely in other shallow-water coastal systems worldwide given continued global warming.



========================================================================== Although there have been several previous studies of overall warming
trends in estuaries (including the Chesapeake Bay), Mazzini and Pianca's research is the first study of marine heat waves in this type of shallow coastal ecosystem.

Their findings not only enhance our basic understanding of these events
but can be used to better predict future occurrences and guide management decisions.

Says Pianca, "Future management decisions should focus not only on the
effect of long-term temperature changes, but also consider these short,
acute events, which could have severe impacts long after they end."
Causes of Bay heat waves In addition to studying the characteristics of
Bay heat waves and how they might be changing through time, Mazzini and
Pianca set out to examine the causes of these extreme events by analyzing
three potential and interacting triggers: heating by the atmosphere,
input of warm river water, and incursions of balmy seawater.

The researchers approached this puzzle by comparing the timing of marine
heat waves both inside and outside the Bay, hypothesizing that heat-wave
events with similar start and end dates are likely to share the same
cause. For water temperatures outside the Bay, they analyzed data from
two ocean observation buoys, one just seaward of the Bay mouth -- within
a current system known as the Bay plume -- and another farther north on
the continental shelf.



========================================================================== Their results show that marine heat waves tend to occur at roughly the
same time both along the entire length of the Bay and within nearby
coastal waters.

They also found a clear correlation between the increased frequency of
marine heat waves and the long-term warming of Bay and coastal waters
observed in other studies. What they did not find was a pattern of heat
waves starting in the Bay and propagating into the ocean, or starting
in the ocean and propagating into the Bay.

Mazzini says these findings "demonstrate a strong connection among these different environments" and point to "coherent large-scale forcing"
as the main driver of marine heat waves in the Bay region. Drawing on
another recent VIMS study, this one of long-term Bay warming, Mazzini says
"the most likely candidate to drive the largely coherent marine heat
waves in the Bay and plume- ocean region is the transfer of heat from
the atmosphere to the water surface." A better understanding of the
causes of Bay heat waves will improve projections of future conditions
and help managers better assess water-quality goals, particularly as
they relate to efforts to limit low-oxygen "dead zones," which can
stress mobile animals such as striped bass, and kill attached or slow-
moving invertebrates outright.

"The future increase in marine heat waves as suggested in our study could aggravate hypoxia in the Bay by further stratifying the water column, increasing the oxygen needed by marine life, and decreasing oxygen
solubility." These changes, warns Mazzini, "could push the Chesapeake
Bay ecosystem past a dangerous tipping point." Concerns regarding the
impact of warming on Bay health and restoration goals were emphasized
earlier this year when the Chesapeake Bay Executive Council signed a
new directive for collective action to address the threats of climate
change in all aspects of the partnership's work.

========================================================================== Story Source: Materials provided by
Virginia_Institute_of_Marine_Science. Original written by David
Malmquist. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Piero L. F. Mazzini, Cassia Pianca. Marine Heatwaves in the
Chesapeake
Bay. Frontiers in Marine Science, 2022; 8 DOI:
10.3389/fmars.2021.750265 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220118125136.htm

--- up 6 weeks, 3 days, 7 hours, 13 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)