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Explanations

Melting icebergs feed a trail of phytoplankton in their wake

Andy Day

29th November 2017

Concern at large blocks of ice-sheet breaking off from the perimeter of Antarctica and icebergs calving off glaciers emerging from the Greenland ice-sheet are worrying indicators of rising global temperatures. But recent studies suggest icebergs 'fertilise' the surrounding ocean with key chemicals that stimulate the growth of phytoplankton. Their growth absorbs carbon dioxide and nicely illustrates a negative feedback effect and transfers between carbon stores.

Recent surveys of patterns of phytoplankton in the wake of iceberg movements has led marine biologists to conclude that as icebergs melt, they fertilise the surrounding waters with iron and trace elements eroded from land surfaces as ice grinds its way towards the coastlines of Antarctica and Greenland. The chemical-rich waters trail icebergs as they melt and stimulate the growth of phytoplankton - the photosynthesising marine organisms that absorb carbon dioxide from the surface waters of the ocean. These are in turn fed upon by tiny marine animals - zooplankton - that produce waste as well as organic remains that sinks into the deeper ocean when they die. 'Marine snow' is the term give for the slow descent of carbon-rich detritus. Most of this is carried by deep ocean currents for thousands of miles, eventually up-welling at a continental shelf to provide nutrient-rich waters for more marine life. But a small proportion falls to the ocean floor and becomes an accumulating store of carbon-based sediments that can be incorporated into the ocean lithosphere. This forms a long-term carbon sink. So: more icebergs; more phytoplankton; and more carbon on the ocean floor - a negative feedback effect dampening down the initial impact of rising global temperatures from the increase in atmospheric carbon. What now needs to be studied is the rate and volume of this effect and whether it will be a measurable - or only very minor - effect on the inexorable rise of atmospheric carbon.

Read more about the plankton restaurants at the end of the iceberg wake in this article of 'Oceanbites' from the University of Rhode Island, and this lengthier, more technical article from 'theConversation'.

Andy Day

Andy recently finished being a classroom geographer after 35 years at two schools in East Yorkshire as head of geography, head of the humanities faculty and director of the humanities specialism. He has written extensively about teaching and geography - with articles in the TES, Geography GCSE Wideworld and Teaching Geography.

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