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Protecting the global ocean for biodiversity, food and climate

Abstract.

"The ocean contains unique biodiversity, provides valuable food resources and is a major sink for anthropogenic carbon. Marine protected areas (MPAs) are an effective tool for restoring ocean biodiversity and ecosystem services1,2, but at present only 2.7% of the ocean is highly protected3. This low level of ocean protection is due largely to conflicts with fisheries and other extractive uses. To address this issue[...]"

 

Source: Nature
Authors: Enric Sala et al.
DOI: https://doi.org/10.1038/s41586-021-03371-z

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Ocean acidification may slow the pace of tropicalization of temperate fish communities

Abstract.

"Poleward range extensions by warm-adapted sea urchins are switching temperate marine ecosystems from kelp-dominated to barren-dominated systems that favour the establishment of range-extending tropical fishes. Yet, such tropicalization may be buffered by ocean acidification, which reduces urchin grazing performance and the urchin barrens that tropical range-extending fishes prefer.[...]"

 

Source: Nature Climate Change
Authors: Ericka O. C. Coni et al.
DOI: https://doi.org/10.1038/s41558-020-00980-w

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Investigating the Roles of External Forcing and Ocean Circulation on the Atlantic Multidecadal SST Variability in a Large Ensemble Climate Model Hiera

Abstract.

"This paper attempts to enhance our understanding of the causes of Atlantic Multidecadal Variability, the AMV. Following the literature, we define the AMV as the SST averaged over the North Atlantic basin, linearly detrended and low-pass filtered. There is an ongoing debate about the drivers of the AMV, which include internal variability generated from the ocean or atmosphere (or both), and external radiative forcing. We test the role of these factors in explaining the time history, variance, and spatial pattern of the AMV using[...]"

 

Source: American Meteorological Soceity 
Authors: Lisa N. Murphy et al.
DOI: https://doi.org/10.1175/JCLI-D-20-0167.1

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Current Atlantic Meridional Overturning Circulation weakest in last millennium

Abstract.

"The Atlantic Meridional Overturning Circulation (AMOC)—one of Earth’s major ocean circulation systems—redistributes heat on our planet and has a major impact on climate. Here, we compare a variety of published proxy records to reconstruct the evolution of the AMOC since about AD 400. A fairly consistent picture of the AMOC emerges: after a long and relatively stable period, there was an initial weakening starting in the nineteenth century, followed by a second, more rapid, decline in the mid-twentieth[...]"

 

Source: Nature Geosciences
Authors: L. Caesar et al.
DOI: https://doi.org/10.1038/s41561-021-00699-z

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Mixing by Oceanic Lee Waves

Abstract.

"Oceanic lee waves are generated in the deep stratified ocean by the flow of ocean currents over sea floor topography, and when they break, they can lead to mixing in the stably stratified ocean interior. While the theory of linear lee waves is well established, the nonlinear mechanisms leading to mixing are still under investigation. Tidally driven lee waves have long been observed in the ocean, along with associated mixing, but observations of lee waves forced by geostrophic eddies are relatively sparse and largely indirect[...]"

 

Source: Annual Reviews
Authors: Sonya Legg
DOI: https://doi.org/10.1146/annurev-fluid-051220-043904

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Multi‐Century Impacts of Ice Sheet Retreat on Sea Level and Ocean Tides in Hudson Bay

Abstract.

"Past and modern large‐scale ice sheet loss results in geographically variable sea level changes. At present, in Hudson Bay, Canada, sea level is decreasing due to glacial isostatic adjustment, which represents a departure from the globally averaged sea level rise. However, there are large uncertainties in future sea level trends with further polar ice sheet retreat in the coming centuries. Sea level changes affect ocean tides considerably because tides are highly sensitive to changes in bathymetry. Here, we present multi‐century sea level projections associated with a suite of past and future ice loss scenarios and consider the impact of these changes on ocean tides[...]"

Source: Advancing Earth and Space Science
Authors: A.‐M. Hayden et al.
DOI: https://doi.org/10.1029/2019JC015104

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Ideas and perspectives: A strategic assessment of methane and nitrous oxide measurements in the marine environment

Abstract.

"In the current era of rapid climate change, accurate characterization of climate-relevant gas dynamics – namely production, consumption, and net emissions – is required for all biomes, especially those ecosystems most susceptible to the impact of change. Marine environments include regions that act as net sources or sinks for numerous climate-active trace gases including methane (CH4) and nitrous oxide (N2O). The temporal and spatial distributions of CH4 and N2O are controlled by the interaction of complex biogeochemical and physical processes. To evaluate and quantify how these mechanisms affect marine CH4 and N2O cycling requires a combination of traditional scientific disciplines including oceanography, microbiology, and numerical modeling[...]"

Source: Biogeosciences
Authors: Samuel T. Wilson et al.
DOI: https://doi.org/10.5194/bg-17-5809-2020

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Organic matter composition and heterotrophic bacterial activity at declining summer sea ice in the central Arctic Ocean

Abstract.

"The Arctic Ocean is highly susceptible to climate change as evidenced by rapid warming and the drastic loss of sea ice during summer. The consequences of these environmental changes for the microbial cycling of organic matter are largely unexplored. Here, we investigated the distribution and composition of dissolved organic matter (DOM) along with heterotrophic bacterial activity in seawater and sea ice of the Eurasian Basin at the time of the record ice minimum in 2012. Bacteria in seawater were highly responsive to fresh organic matter and remineralized on average 55% of primary production in the upper mixed layer. Correlation analysis showed that the accumulation of dissolved combined carbohydrates (DCCHO) and dissolved[...]"

 

Source: Association for the Sciences Limnology and Oceanography
Authors: Judith Piontek et al.
DOI: https://doi.org/10.1002/lno.11639

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Increasing ocean stratification over the past half-century

Abstract.

"Seawater generally forms stratified layers with lighter waters near the surface and denser waters at greater depth. This stable configuration acts as a barrier to water mixing that impacts the efficiency of vertical exchanges of heat, carbon, oxygen and other constituents. Previous quantification of stratification change has been limited to simple differencing of surface and 200-m depth changes and has neglected the spatial complexity of ocean density change. Here, we quantify changes in ocean stratification down[...]"

 

Source: Nature Climate Change
Authors: Guancheng Li  et al.
DOI: https://doi.org/10.1038/s41558-020-00918-2

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Observing the Global Ocean with Biogeochemical-Argo

Abstract.

"Biogeochemical-Argo (BGC-Argo) is a network of profiling floats carrying sensors that enable observation of as many as six essential biogeochemical and bio-optical variables: oxygen, nitrate, pH, chlorophyll a, suspended particles, and downwelling irradiance. This sensor network represents today's most promising strategy for collecting temporally and vertically resolved observations of biogeochemical properties throughout the ocean. All data are freely available within 24 hours of transmission. These data fill large gaps in ocean-observing systems and support three ambitions: gaining a better understanding of biogeochemical processes (e.g., the biological[...]"

 

Source: Annual Review of Marine Science
Authors: Hervé Claustre et al.
DOI: https://doi.org/10.1146/annurev-marine-010419-010956

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