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Recent Acceleration Seen in Chemical and Physical Changes in the Ocean


From L to R: Rod Johnson (BATS Co-PI), Emily Davey (Research Technical), Dom Smith (Research Technical) and Claire Medley (Research Technology) tested CTD for soluble O2 and CO2 aboard the R / V Atlantic Explorer during a regular Bermuda Atlantic Time-series Study (BATS) cruise. Credit: Ella Cedarhold, Bermuda Institute of Ocean Science

Two open-Ocean hydrographic stations that recorded 40 years of change in the subtropical North Atlantic Ocean.

New research published in Communications to Nature Earth and Environment today (October 1

6, 2020) uses data from two sustainable open-ocean hydrographic stations in the North Atlantic near Bermuda to reflect recent changes in ocean physics and chemistry since 1980. The study shows the difference decadal changes and recent acceleration of surface heating, salinification, deoxygenation, and carbon dioxide (CO) changes2) -carbonate chemistry that drives ocean acidity.

The study used datasets from Hydrostation ‘S’ and Bermuda Atlantic Time-series Study (BATS) projects at the Bermuda Institute of Ocean Science (BIOS). Both were led by Professor Nicholas Bates, senior BIOS scientist and chief investigator (PI) of the projects, and Rod Johnson, assistant BIOS scientist and co-PI of the projects. Together, this time series represents the two longest continuous data records from the global open ocean.

“Four decades of data from BATS and Hydrostation ‘S’ show that the oceans do not change evenly over time and that carbon dioxide has been unstable over time with variation from decade to decade, “Bates said.

BIOS BATS Validation Cruise Pump

From L to R: Ella Cedarhold (Marine Technician), Claire Medley (Research Technician), Emily Davey (Research Technician), and Lydia Sgouros (Marine Techician) disperse in-situ pump from R / V Atlantic Explorer for proteomics samples during a recent Bermuda Atlantic Time-series Study (BATS) cruise. Credit: Bermuda Institute of Ocean Science

At the two sites, Hydrostation ‘S’ is the oldest, located approximately 15 miles (25 km) southeast of Bermuda and consists of repeated biweekly hydrographic observations of temperature, salinity, and dissolved oxygen. by water column since 1954. The Bermuda Atlantic The Time-series Study (BATS) site is located approximately 50 miles (80 km) southeast of Bermuda. It consists of monthly sampling of the physics, chemistry, and biology of the entire water column since 1988. The study datasets represent more than 1381 trips to Hydrostation ‘S’ from 1954 to 2020 and beyond. on 450 trips to BATS from 1988 until the end of 2019.

The results show that, in the last 40 years, the surface temperature of the Sargasso Sea has risen by 0.85 +/- 0.12oC, with temperatures over the summer rising at a higher rate than in winter. Additionally, the winter (<22 ° C) ocean state becomes shorter by almost a month, while summer (with warmer water than 25 ° C) lasts. At the same time, the surface salinity also increased by ~ 0.11 +/- 0.02. Importantly, these data provide evidence of decadal diversity; however, in the last decade (2010-2019), rapid warming of 1.18oC and salinification of 0.14 occurred.

The data also shows a trend of melting oxygen (DO) declining in the Sargasso Sea since 1980, representing a loss of 22% per decade. Given the ocean warming observed in the Sargasso Sea, researchers estimate that the warming effect on DO solubility has likely contributed to nearly 13% of DO’s total decline over the past nearly 40 years. The remaining deoxygenation (~ 87%) should have resulted from the combined effect of changes in marine biology and physics.

Time-series data BATS and Hydrostation ‘S’ enables direct detection of ocean acidification signal in North Atlantic waters. The typical pH range of surface waters in the 1980s ranged from a winter high of ~ 8.2 to a summer summer of ~ 8.08-8.10, with the remaining slightly alkaline ocean at present (~ 7.98- 8.05). The pH change rate is ~ 0.0019 +/- 0.0001 year-1, which is a more negative rate than previously reported and represents a 20% increase in hydrogen ion concentration since 1983. These changes are accompanied by a significant increase in molten inorganic carbon and CO2 and decreases in both states of saturite and aragonite saturation.

“For forty years, sea water CO2-carbonate chemistry conditions have now changed beyond the seasonal chemical changes observed in the 1980s, “Johnson said.” The change in sea water CO2 -continue carbonate chemistry in future anthropogenic CO2 emissions. “

Observations in Bermuda show significant decadal diversity and emphasize the need for long-term data to determine trends in other physical and biogeochemical characteristics of the ocean, especially when linking local dimensions to metric changes. Long-term ocean chemistry and physical data from time series sites such as Hydrostation ‘S’ and BATS provide critical and unparalleled observations that, when combined with marine environment models, allow a more complete understanding of global carbon cycle drivers

Reference: “Accelerating ocean warming, salinification, deoxygenation and acidification over the subtropical North Atlantic Ocean” by Nicholas Robert Bates and Rodney J. Johnson, 16 October 2020, Communication World and Environment.
DOI: 10.1038 / s43247-020-00030-5

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