Abstract
Prolonged events of anomalously warm sea water temperature, or marine heatwaves (MHWs), have major detrimental effects to marine ecosystems and the world's economy. While frequency, duration and intensity of MHWs have been observed to increase in the global oceans, little is known about their potential occurrence and variability in estuarine systems due to limited data in these environments. In the present study we analyzed a novel data set with over three decades of continuous in situ temperature records to investigate MHWs in the largest and most productive estuary in the US: the Chesapeake Bay. MHWs occurred on average twice per year and lasted 11 days, resulting in 22 MHW days per year in the bay. Average intensities of MHWs were 3°C, with maximum peaks varying between 6 and 8°C, and yearly cumulative intensities of 72°C × days on average. Large co-occurrence of MHW events was observed between different regions of the bay (50–65%), and also between Chesapeake Bay and the Mid-Atlantic Bight (40–50%). These large co-occurrences, with relatively short lags (2–5 days), suggest that coherent large-scale air-sea heat flux is the dominant driver of MHWs in this region. MHWs were also linked to large-scale climate modes of variability: enhancement of MHW days in the Upper Bay were associated with the positive phase of Niño 1+2, while enhancement and suppression of MHW days in both the Mid and Lower Bay were associated with positive and negative phases of North Atlantic Oscillation, respectively. Finally, as a result of long-term warming of the Chesapeake Bay, significant trends were detected for MHW frequency, MHW days and yearly cumulative intensity. If these trends persist, by the end of the century the Chesapeake Bay will reach a semi-permanent MHW state, when extreme temperatures will be present over half of the year, and thus could have devastating impacts to the bay ecosystem, exacerbating eutrophication, increasing the severity of hypoxic events, killing benthic communities, causing shifts in species composition and decline in important commercial fishery species. Improving our basic understanding of MHWs in estuarine regions is necessary for their future predictability and to guide management decisions in these valuable environments.
Highlights
Analogous to the well studied heatwaves in the atmosphere (e.g., Perkins, 2015), prolonged anomalously warm events occur in the ocean, and are referred to as Marine Heatwaves (MHWs)
Duration and intensity of marine heatwaves (MHWs) have been observed to increase in the global oceans over the past decades (Oliver et al, 2018), and due to long-term ocean warming under climate change, this trend is expected to further increase in the future (Frölicher and Laufkötter, 2018; Oliver et al, 2019)
A total of eight stations were selected (Figure 1), six inside the Chesapeake Bay: Tolchester Beach (TB) and Thomas Point (TP) located in the Upper Bay (UB), Solomons Island (SI) and Lewisetta (LW) in the Mid Bay (MB), Goodwin Islands (GI) and Kiptopeke (KP) in the Lower Bay (LB); and two in the Mid-Atlantic Bight (MAB) mid-shelf: Chesapeake Light Tower (CHL) located 26 km offshore of the CB mouth, at the transition zone between the estuary and coastal ocean, an area influenced by the CB plume (e.g., Boicourt, 1973; Brian Dzwonkowski and Yan, 2005; Valle-Levinson et al, 2007; Jiang and Xia, 2016; Mazzini et al, 2019), and Delaware Bay buoy (DEB) located 198 km north of the CB mouth and 30 km offshore from the coast
Summary
Analogous to the well studied heatwaves in the atmosphere (e.g., Perkins, 2015), prolonged anomalously warm events occur in the ocean, and are referred to as Marine Heatwaves (MHWs). Notable MHW events have been associated with record-breaking harmful algal blooms (McCabe et al, 2016; Gobler, 2020; Trainer et al, 2020), have led to global-scale coral bleaching (Hughes et al, 2017; Eakin et al, 2019), geographical species shifts and changes in species composition (Ehlers et al, 2008; Cavole et al, 2016; Sanford et al, 2019), mortality of kelps, submerged aquatic vegetation (SAV), invertebrates (Moore and Jarvis, 2008; Garrabou et al, 2009; Marb and Duarte, 2010; Fraser et al, 2014; Thomson et al, 2015; Wernberg et al, 2016; Shields et al, 2018, 2019; Seuront et al, 2019; Thomsen et al, 2019; Filbee-Dexter et al, 2020; Aoki et al, 2021; Johnson et al, 2021), and impacted commercial fisheries and aquaculture (Mills et al, 2013; Caputi et al, 2016; Oliver et al, 2017; Jacox, 2019). While the satellite data products used in those studies can resolve open ocean and shelf scales (e.g., Marin et al, 2021), because of their relative coarse resolution (∼25 km) they typically fail to resolve most estuarine systems, which are characterized by having complex shorelines and reduced spatial scales
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