Arctic Nutrient Balance
The first study of its kind to calculate the amount of nutrients entering and leaving the Arctic Ocean has been carried out by scientists based at the National Oceanography Center, Southampton. Their results, which are published this month in the Journal of Geophysical Research, show that there is a mismatch between what goes into the Arctic Ocean and what comes out. This is the first study to look at the transport of dissolved inorganic nutrients nitrate, phosphate and silicate together, all of which are essential for life in the ocean. The study combined measurements of nutrient concentrations with measurements of how much water was transported across the main Arctic gateways — Davis Strait, Fram Strait, the Barents Sea Opening and Bering Strait during the summer of 2005.
Variations in nutrient availability in the world’s oceans could be a vital component of future environmental change, according to a related multi-author review paper involving the National Oceanography Center, Southampton (NOCS).
This paper, published Nature Geoscience, reviews what we know about ocean nutrient patterns and interactions, and how they might be influenced by future climate change and other man-made factors. The authors also highlight how nutrient cycles influence climate by fueling biological production, hence keeping carbon dioxide (CO2) locked down in the ocean away from the atmosphere.
As for the Arctic Ocean imbalance growth of the tiny plants at the base of marine food chains, microalgae, in the Arctic Ocean is fuelled by nutrient inputs from the Pacific and Atlantic Oceans, and from rivers around the Arctic Ocean rim. These riverine inputs are increasing as a result of increasing temperatures, because nutrients previously locked up in frozen soils — or permafrost — are being released as the permafrost thaws.
In the study, the researchers looked at all oceanic inputs and outputs of the three nutrients. They found that the nitrate coming into the Arctic Ocean balanced how much goes out. But for silicate and phosphate, more goes out into the North Atlantic than comes into the Arctic Ocean.
"Firstly, the imbalances indicate that the Arctic Ocean is an important source of phosphate and silicate to the North Atlantic. Secondly, while nitrate transports are balanced, in the Arctic large amounts of nitrogen are lost to the atmosphere as nitrogen gas through a process called denitrification."
So where do the extra nutrients come from? "Data suggest that rivers can provide most of the silicate that is transported to the North Atlantic, which implies that further alterations on Arctic river nutrient loads will have a direct impact on nutrient transports to the Atlantic.
"In the case of nitrate and phosphate, no obvious sources seem to provide enough to offset the imbalance. We are therefore investigating the possibility that the extra nitrate and phosphate comes from dissolved organic matter — the decaying remains of microorganisms in the ocean and decaying remains from soils in river loads.
The broad implication is that the nutrient flow from the Arctic may influence other more southern oceans and their life contents. Everything seems to effect everything else in a world wide bio balance. Understanding how the relative limitation of nitrogen and phosphorus in the arctic is influenced by temperature is essential to the long-term understanding of how global warming may influence ecosystem processes such as decomposition, nutrient mineralization and vegetation response in this region and the whole world.
Arctic landscape image via Shutterstock.