New research into the chemistry of the oceans during ice ages is helping to solve a puzzle that has engaged scientists for more than two decades.
(From University of Tasmania) — At issue is how much of the CO2 that entered the ocean during ice ages can be attributed to the ‘biological pump’, where atmospheric carbon is absorbed by phytoplankton and sequestered to the seafloor as organisms die and sink.
Solving the puzzle is important to improve the accuracy of climate models and inform understanding of how ocean processes may react to future climate change.
Led by IMAS and University of Liverpool scientists and published in Nature Communications, the study found ice age phytoplankton in the tropics absorbed high levels of CO2 due to fertilisation by iron-rich dust blowing into the ocean. Lead author Dr Pearse Buchanan said that until now models had only been able to explain a portion of the CO2 that entered ice age oceans via the biological pump.
“During past ice ages, carbon levels were lower in the atmosphere and higher in the oceans than today, but scientific models aren’t able to account for all of the additional CO2 that entered the ocean,” Dr Buchanan said. “The leading hypothesis has been that iron-rich dust blown from glacial landscapes stimulated phytoplankton growth in high latitudes, but this only explained around one-third of the extra CO2 absorbed through the biological pump: the other two-thirds was effectively ‘missing’. “We used an ocean model to look at the response to iron rich dust of phytoplankton in tropical waters, particularly a group of phytoplankton called “nitrogen fixers.”
“These are able to biochemically ‘fix’ nitrogen from the atmosphere, much like nitrogen fixing bacteria that help legume crops thrive in nutrient poor soil. Marine nitrogen fixers are known to be important in the marine nitrogen cycle, and now we’ve shown they’re also critically important in the marine carbon cycle. “When we added iron to our ocean model…
Read the full article here: https://www.sciencedaily.com/releases/2019/10/191010095755.htm