Extent and Magnitude of Subsurface Anomalies During the Northeast Pacific Blob as Measured by Animal‐Borne Sensors

Abstract

Marine heatwaves (MHWs) are prolonged warm water events that are increasing in frequency and magnitude due to rising global temperatures. The Northeast Pacific Blob was an unusually widespread MHW that affected ecosystems across the Northeast Pacific, from producers to top predators. Temperature and salinity data collected by northern elephant seals (Mirounga angustirostris) from 2014 to 2017 show significant (>2 sd) warm anomalies throughout the top 1,000 m of the water column, with peak warming in late 2015. Using temperature and salinity as a tracer of layers of constant density, we looked at how lateral advection may have contributed to the development of the Blob. Temperature and salinity anomalies and the expansion of the water column at the base of the pycnocline both indicate that northward advection of warm, salty water played an important role in the observed accumulation of warm water, in addition to surface warming. These findings contribute to our understanding of the physical dynamics of the Blob, especially the thermal content and structure of the water column, and offer mechanisms for its formation and maintenance, which are crucial to assessing the ecological effects of MHWs now and in the future.

Echoes of the 2013–2015 Marine Heat Wave in the Eastern Bering Sea and Consequent Biological Responses

“…The Blob lasted through 2016 in the upper 0-100-m layer yet lingered through 2017-2018 in the subsurface 100-200-m layer as documented by Freeland and Ross (2019), who also noted a possible return in late 2018 of a warm anomaly (Figure 3), which actually occurred in 2019 as reported by Scannell et al (2020). During the first years, The Blob's manifestation in the surface layer diminished, while its manifestation in the subsurface markedly increased as noted by Freeland and Ross (2019), Zhi et al (2019), and Holser et al (2022), among others (Figure 3). The Blob's impact on the marine ecology of the Northeast Pacific was dramatic in terms of magnitude, duration, and spatial extent.…”

“…The stratification barrier notwithstanding, The Blob gradually extended to the subsurface over 2014-2016 as documented by Freeland and Ross (2019). Temperature and salinity data collected in 2014-2017 by instrumented northern elephant seals in the NE Pacific were analyzed by Holser et al (2022) to provide evidence of The Blob extending eventually to 1000 m depth. The vertical extent of The Blob is essential with regard to its propagation to the Bering Sea via the Aleutian Straits where the shallow depths of some passes will constrain water transport as discussed below; for more information see the latest geomorphological study of the Aleutian passes by Zimmerman and Prescott (2021).…”

On the Vertical Structure and Propagation of Marine Heatwaves in the Eastern Pacific

“…Scannell et al. (2020) demonstrated that the heat anomalies from this event were lingering for years at depth, affecting ecosystems for much longer periods than diagnosed from the surface only (see also Freeland & Ross, 2019; Holser et al., 2022; Jackson et al., 2018). Due to the wide spacing ($$\mathcal{O}$$ of 100 km) of the Argo float profiles and their 10 days repeat cycle, these authors had to average the data considerably in time and space, thereby losing much detail.…”

“…Similarly, Johnson et al (2022) and Scannell et al (2020) used Argo float data to investigate the vertical extent and propagation of the Northeast Pacific Blob heatwave, that is, the strong surface MHW in the Northeastern Pacific that lasted for multiple years ( , Bond et al, 2015Di Lorenzo & Mantua, 2016) and was likely even a compound extreme (Gruber et al, 2021). Scannell et al (2020) demonstrated that the heat anomalies from this event were lingering for years at depth, affecting ecosystems for much longer periods than diagnosed from the surface only (see also Freeland & Ross, 2019;Holser et al, 2022;Jackson et al, 2018). Due to the wide spacing ( 𝐴𝐴  of 100 km) of the Argo float profiles and their 10 days repeat cycle, these authors had to average the data considerably in time and space, thereby losing much detail.…”

Impacts of Marine Heatwaves on Subsurface Temperatures and Dissolved Oxygen in the Chesapeake Bay

“…Nevertheless, a few noteworthy studies (e.g., Hu et al., 2021; Schaeffer & Roughan, 2017) have been able to identify MHWs in the subsurface using observations from buoys with daily temperature data (though such records are rare) and with hindcast models (Amaya et al., 2023a; Chen et al., 2015; Großelindemann et al., 2022; Oliver et al., 2018; Ryan et al., 2021). Additionally, less frequently sampled data sets (i.e., Argo floats, animal mounted sensors, and CTD casts), have been used to examine the subsurface temperature anomalies during identified surface events, allowing for an initial look at the subsurface temperature structure associated with MHWs (Elzahaby & Schaeffer, 2019; Freeland & Ross, 2019; Holser et al., 2022; Jackson et al., 2018; Scannell et al., 2020). These studies have shown that MHWs in the global oceans have the potential to last longer and at a greater intensity (e.g., positive temperature anomalies) than what is indicated by their surface signature, thereby increasing the potential impact on marine ecosystems.…”