Increasing ocean stratification over the past half-century

Li, Guancheng; Cheng, Lijing; Zhu, Jiang; Trenberth, Kevin E.; Mann, Michael; Abraham, John

doi:10.1038/s41558-020-00918-2

Cited by 263 publications

(172 citation statements)

References 52 publications

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“…This persistence of subsurface heat and the possible seasonal reemergence of surface anomalies could in fact help supercharge the occurrence of multiyear events. As future warming trends favor a more stratified upper ocean (Li et al, 2020), we expect that detrainment out of the mixed layer may become less effective in storing MHW anomalies in the subsurface and therefore further amplify surface warming. This possibility is concerning owing to the impacts that accumulated heat stress and stratification have on pelagic marine ecosystems and primary production (Cavole et al, 2016;Jacox et al, 2016;Smale et al, 2019).…”

Section: Discussionmentioning

confidence: 99%

Subsurface Evolution and Persistence of Marine Heatwaves in the Northeast Pacific

Scannell

Johnson

Thompson

et al. 2020

Geophysical Research Letters

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The reappearance of a northeast Pacific marine heatwave (MHW) sounded alarms in late summer 2019 for a warming event on par with the 2013-2016 MHW known as The Blob. Despite these two events having similar magnitudes in surface warming, differences in seasonality and salinity distinguish their evolutions. We compare and contrast the ocean's role in the evolution and persistence of the 2013-2016 and 2019-2020 MHWs using mapped temperature and salinity data from Argo floats. An unusual near-surface freshwater anomaly in the Gulf of Alaska during 2019 increased the stability of the water column, preventing the MHW from penetrating deep as strongly as the 2013-2016 event. This freshwater anomaly likely contributed to the intensification of the MHW by increasing the near-surface buoyancy. The gradual buildup of subsurface heat content throughout 2020 in the region suggests the potential for persistent ecological impacts. Plain Language Summary Surface marine heatwaves (MHWs) are periods of prolonged and extremely warm regional sea surface temperature that can negatively impact the health and productivity of marine ecosystems. Using surface and subsurface ocean observations, we compare and contrast two recent MHWs to show that salinity variations play an important role in the vertical distribution of temperature anomalies by changing the overall stability of the water column. During the 2019-2020 MHW, the near-surface waters in the Gulf of Alaska were fresher than normal, preventing warm sea surface temperatures from mixing as deeply into the subsurface as in the 2013-2016 MHW. The freshening in 2019 likely enhanced warming in the buoyant surface layer. As warmer temperatures gradually mix downward they can persist long after the surface MHW disappears, suggesting that the ocean can provide memory for long-lived MHWs. The subsurface persistence of MHWs has potential ramifications for long-lasting ecological impacts.

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Section: Discussionmentioning

confidence: 99%

Subsurface Evolution and Persistence of Marine Heatwaves in the Northeast Pacific

Scannell

Johnson

Thompson

et al. 2020

Geophysical Research Letters

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“…2 a. A recent study by Li et al 36 provided evidence of a substantial 5.3% increase of stratification ( , buoyancy frequency) over 2000 m and 6.9% in the upper 200 m over the period 1960–2018 globally. These authors noted a 4.1% increase of stratification for the whole Atlantic basin up to 2000 m, and the slope and shelf region in the Atlantic has seen an even more dramatic increase.…”

Section: Discussionmentioning

confidence: 93%

Interannual and seasonal asymmetries in Gulf Stream Ring Formations from 1980 to 2019

Silver

Gangopadhyay

Gawarkiewicz

et al. 2021

Sci Rep

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As the Gulf Stream separates from the coast, it sheds both Warm and Cold Core Rings between $$75^\circ$$ 75 ∘ and $$55^\circ \,\hbox {W}$$ 55 ∘ W . We present evidence that this ring formation behavior has been asymmetric over both interannual and seasonal time-scales. After a previously reported regime-shift in 2000, 15 more Warm Core Rings have been forming yearly compared to 1980–1999. In contrast, there have been no changes in the annual formation rate of the Cold Core Rings. This increase in Warm Core Ring production leads to an excess heat transfer of 0.10 PW to the Slope Sea, amounting to 7.7–12.4% of the total Gulf Stream heat transport, or 5.4–7.3% of the global oceanic heat budget at $$30^\circ \,\hbox {N}$$ 30 ∘ N . Seasonally, more Cold Core Rings are produced in the winter and spring and more Warm Core Rings are produced in the summer and fall leading to more summertime heat transfer to the north of the Stream. The seasonal cycle of relative ring formation numbers is strongly correlated (r = 0.82) with that of the difference in upper layer temperatures between the Sargasso and Slope seas. This quantification motivates future efforts to understand the recent increasing influence of the Gulf Stream on the circulation and ecosystem in the western North Atlantic.

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“…For example, stratification has increased, limiting vertical exchange (for example, of nutrients) through the water column by ~5% since 1960 (ref. 7 ). Deoxygenation (where warmer water holds less oxygen and, coupled with changes in stratification and circulation, changes the amount of oxygen entering the deep ocean) has potential wide-ranging effects on fisheries and ecosystems 8 .…”

Section: Wave Of Unitymentioning

confidence: 99%

Wave of unity

2021

Nat. Clim. Chang.

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Increasing ocean stratification over the past half-century

Cited by 263 publications

References 52 publications

Subsurface Evolution and Persistence of Marine Heatwaves in the Northeast Pacific

Subsurface Evolution and Persistence of Marine Heatwaves in the Northeast Pacific

Interannual and seasonal asymmetries in Gulf Stream Ring Formations from 1980 to 2019

Wave of unity

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