Climate change has wrought major changes to ocean stability faster than previously thought, according to a recent study, raising alarms over its role as a global thermostat and the marine life it supports.
The research published in the journal Nature looked at 50 years of data and followed the way in which surface water “decouples” from the deeper ocean.
Climate change has disrupted ocean mixing, a process that helps store away most of the world’s excess heat and a significant proportion of CO2.
Water on the surface is warmer — and therefore less dense — than the water below, a contrast that is intensified by climate change.
Global warming is also causing massive amounts of fresh water to flush into the seas from melting ice sheets and glaciers, lowering the salinity of the upper layer and further reducing its density.
This increasing contrast between the density of the ocean layers makes mixing harder, so oxygen, heat and carbon are all less able to penetrate to the deep seas.
Study on calcifying plankton and climate change published in Nature Climate Change
The global increase in atmospheric carbon dioxide concentration is potentially threatening marine biodiversity in two ways. First, carbon dioxide and other greenhouse gases accumulating in the atmosphere are causing global warming. Second, carbon dioxide is altering sea water chemistry, making the ocean more acidic.
Although temperature has a cardinal influence on all biological processes from the molecular to the ecosystem level, acidification might impair the process of calcification or exacerbate dissolution of calcifying organisms.
Here, we show however that North Atlantic calcifying plankton primarily responded to climate-induced changes in temperatures during the period 1960–2009, overriding the signal from the effects of ocean acidification. We provide evidence that foraminifers, coccolithophores, both pteropod and non-pteropod molluscs and echinoderms exhibited an abrupt shift circa 1996 at a time of a substantial increase in temperature and that some taxa exhibited a poleward movement in agreement with expected biogeographical changes under sea temperature warming. Although acidification may become a serious threat to marine calcifying organisms, our results suggest that over the study period the primary driver of North Atlantic calcifying plankton was oceanic temperature.