New analysis of two decades of estuary data shows that marine heatwaves are frequently embedded in extended warm periods. Conventional metrics undercount cumulative heat exposure by roughly 150% on average, with one-third of events producing three times more total heat than the peak window alone.
Conventional MHW measures miss most of the thermal exposure: total heat exposure is underestimated by more than 150% on average when warming before and after heatwaves is excluded.
Researchers analyzed 2,580 marine heatwaves recorded in 20 U.S. estuaries over two decades to build a framework that treats heatwaves as part of longer warming episodes.
Two event types appear: about two-thirds are 'individual' with ~60 days of surrounding warming, and about one-third are 'compound' with ~90 days of pre- and post-warming that add more than three times the cumulative heat of the MHW itself.
Marine heatwaves may be only the most intense part of much longer warming events, with elevated temperatures sometimes lingering for months. Researchers found that conventional measurements underestimate total heat exposure by more than 150% on average, potentially overlooking a major source of stress on marine ecosystems. Facebook Twitter Pinterest LinkedIN Email FULL STORY Marine heatwaves are often treated as isolated bursts of extreme warmth, but new research shows they can be embedded within much longer periods of elevated temperatures.
"We can no longer look at marine heatwaves in isolation when assessing the impact of warming events on coastal and oceanic ecosystems," said Mazzini. Their analysis found that conventional assessments underestimate total heat exposure by more than 150% on average, a difference that could have important consequences for understanding ecosystem health. "Your risk of sunburn depends on both sunlight intensity and how long you're exposed to it.
Yet marine heatwaves (MHWs) have traditionally been studied as distinct events with clearly defined beginnings and endings. "We started to notice these warm-water anomalies on either side of marine heatwaves and realized that they're actually embedded within larger periods of warm water," explained lead author Ricardo Utzig Nardi M.S. "It sounds obvious, but studies usually focus only on the marine heatwave window and that's not an accurate representation of real-world conditions." Nardi found that these broader stretches of unusually warm water can continue for weeks or even months, with the marine heatwave occurring somewhere within that longer period.
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