Regional Structure in the Marine Heat Wave of Summer 2015 Off the Western United States

Fewings, Melanie R.; Brown, Kevin

doi:10.3389/fmars.2019.00564

Cited by 33 publications

(36 citation statements)

References 67 publications

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“…Our definition for MHWs is similar to that proposed in Hobday et al (2016) with modifications in the length of the climatological period and in the minimum event duration. Owing to the prominence and persistence of the 2013-2016 and 2019-2020 MHWs, our definition highlights the same large-scale features described in previous studies using daily data (e.g., Fewings & Brown, 2019;Gentemann et al, 2017).…”

Section: Discussionmentioning

confidence: 77%

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: 77%

Subsurface Evolution and Persistence of Marine Heatwaves in the Northeast Pacific

Scannell

Johnson

Thompson

et al. 2020

Geophysical Research Letters

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“…Downwelling anomalies persisted throughout most of 2014 and during the upwelling months of 2015. Below average upwelling, and even downwelling during December 2013 and autumn 2014 in NBox, was likely the result of weak coastal winds (Fewings and Brown 2019;Robinson 2016;Zaba and Rudnick 2016). Anomalous alongshore heat advection warmed both volumes from 250 to 0 m in autumn to winter of 2013, as well as NBox in autumn 2014 and SBox in autumn 2015.…”

Section: Discussionmentioning

confidence: 96%

“…This work presents an analysis over 2014-16 of nearsurface circulation and temperature anomalies, as well as the surface heat flux and heat advection anomalies that drove periods of warming. Surface heat flux anomalies have been linked to changes in low cloud cover and downward shortwave radiation (Myers et al 2018), and vertical downwelling anomalies have been linked to local wind forcing (Fewings and Brown 2019;Zaba and Rudnick 2016) and coastally trapped waves (Frischknecht et al 2017). Horizontal heat advection anomalies are more difficult to explain, particularly the alongshore component, because they can be influenced by a combination of atmospheric and oceanic conditions both local and remote.…”

Section: Discussionmentioning

confidence: 99%

Volume and Heat Budgets in the Coastal California Current System: Means, Annual Cycles, and Interannual Anomalies of 2014–16

Zaba

Rudnick

Cornuelle

et al. 2020

Journal of Physical Oceanography

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The data-assimilating California State Estimate (CASE) enables the explicit evaluation of spatiotemporally varying volume and heat budgets in the coastal California Current System (CCS). An analysis of over 10 years of CASE model output diagnoses the physical drivers of the CCS mean state, annual cycles, and the 2014-16 temperature anomalies associated with a marine heat wave and an El Niño event. The largest terms in the mean mixed layer (from250 to 0 m) volume budgets are upward vertical transport at the coast and offshore-flowing ageostrophic Ekman transport at the surface, the two branches of the coastal upwelling overturning cell. Contributions from onshore geostrophic flow in the Southern California Bight and alongshore geostrophic convergence in the central CCS balance the mean volume budgets. The depthdependent annual cycle of vertical velocity exhibits the strongest upward velocity between 240and 230-m depth in April. Interannual volume budgets show that over 50% of the 2013.5-16.5 time period experienced downwelling anomalies, which were balanced predominantly by alongshore transport convergence and, less often, by onshore transport anomalies. Mixed layer temperature anomalies persisted for the entirety of 2014-16, reaching a maximum of 138 in October 2015. The mixed layer heat budget shows that intermittent high air-sea heat flux anomalies and alongshore and vertical heat advection anomalies all contributed to warming during 2014-16. A subsurface (from 2210 to 2100 m) heat budget reveals that in September 2015 anomalous poleward heat advection into the Southern California Bight by the California Undercurrent caused deeper warming during the 2015/16 El Niño.

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“…However, within the California Current, larval fish responses to warming between the north and south are not necessarily congruent (Thompson et al., 2014). Oceanographic conditions were very unusual in California (approximately N 35°–N 41°) with highly anomalous warm water just offshore abutting anomalously cold water against the shoreline (Fewings & Brown, 2019). In fact, this cold‐water intrusion close to shore likely explains the relatively high abundances of cold‐water affinity species observed in the two southern California Current regions closest to the coast during 2015.…”

Section: Discussionmentioning

confidence: 99%

Responses of ichthyoplankton assemblages to the recent marine heatwave and previous climate fluctuations in several Northeast Pacific marine ecosystems

Nielsen

Rogers

Brodeur

et al. 2020

Global Change Biology

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The effects of climate warming on ecosystem dynamics are widespread throughout the world's oceans. In the Northeast Pacific, large‐scale climate patterns such as the El Niño/Southern Oscillation and Pacific Decadal Oscillation, and recently unprecedented warm ocean conditions from 2014 to 2016, referred to as a marine heatwave (MHW), resulted in large‐scale ecosystem changes. Larval fishes quickly respond to environmental variability and are sensitive indicators of ecosystem change. Categorizing ichthyoplankton dynamics across marine ecosystem in the Northeast Pacific can help elucidate the magnitude of assemblage shifts, and whether responses are synchronous or alternatively governed by local responses to regional oceanographic conditions. We analyzed time‐series data of ichthyoplankton abundances from four ecoregions in the Northeast Pacific ranging from subarctic to subtropical: the Gulf of Alaska (1981–2017), British Columbia (2001–2017), Oregon (1998–2017), and the southern California Current (1981–2017). We assessed the impact of the recent (2014–2016) MHW and how ichthyoplankton assemblages responded to past major climate perturbations since 1981 in these ecosystems. Our results indicate that the MHW caused widespread changes in the ichthyoplankton fauna along the coast of the Northeast Pacific Ocean, but impacts differed between marine ecosystems. For example, abundances for most dominant taxa were at all‐time lows since the beginning of sampling in the Gulf of Alaska and British Columbia, while in Oregon and the southern California Current species richness increased as did abundances of species associated with warmer waters. Lastly, species associated with cold waters also increased in abundances close to shore in southern California during the MHW, a pattern that was distinctly different from previous El Niño events. We also found several large‐scale, synchronized ichthyoplankton assemblage composition shifts during past major climate events. Current climate projections suggest that MHWs will become more intense and thus our findings can help project future changes in larval dynamics, allowing for improved ecosystem management decisions.

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Regional Structure in the Marine Heat Wave of Summer 2015 Off the Western United States

Cited by 33 publications

References 67 publications

Subsurface Evolution and Persistence of Marine Heatwaves in the Northeast Pacific

Subsurface Evolution and Persistence of Marine Heatwaves in the Northeast Pacific

Volume and Heat Budgets in the Coastal California Current System: Means, Annual Cycles, and Interannual Anomalies of 2014–16

Responses of ichthyoplankton assemblages to the recent marine heatwave and previous climate fluctuations in several Northeast Pacific marine ecosystems

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