UK Ocean Acidification

The UK Ocean Acidification programme (UKOA) deployed the RRS James Clark Ross to investigate the progression and impacts of the pH decline called ocean acidification that accompanies oceanic CO2 uptake. The first cruise circumnavigated the UK, while the others explored the Atlantic sectors of the Arctic and Southern Oceans. I joined the carbonate chemistry team at sea for the two polar expeditions.

High-latitude carbonate chemistry

One goal of UKOA was to study the processes that control the marine carbonate system in the presence of seasonal sea ice loss in the polar marine environment. We published the results in a UKOA-themed special issue of Deep-Sea Research Part II:

Tynan, E., Clarke, J. S., Humphreys, M. P., Ribas-Ribas, M., Esposito, M., Rérolle, V. M. C., Schlosser, C., Thorpe, S. E., Tyrrell, T. and Achterberg, E. P. (2016). Physical and biogeochemical controls on the variability in surface pH and calcium carbonate saturation states in the Atlantic sectors of the Arctic and Southern Oceans. Deep-Sea Research Part II 127, 7–27. doi:10.1016/j.dsr2.2016.01.001.

We found that proximity to retreating sea ice had different consequences in the north and south hemispheres because of the different circulation and background chemistry of the seawater, as illustrated in the schematic below.

Above: representation of the processes controlling seawater pH and calcium carbonate solubility (Ω) distributions in ice-influenced parts of the Arctic (Fram Strait) and the Southern (Weddell Sea) Oceans (from Tynan et al., 2016).

Polar plankton

The UKOA cruises also observed the plankton communities and we conducted “bioassay” experiments to determine their responses to future environmental change. In these bioassays, different amounts of CO2 were added to seawater samples to represent likely future conditions, and we measured how the plankton in the samples responded. Some related publications:

Poulton, A. J., Daniels, C. J., Esposito, M., Humphreys, M. P., Mitchell, E., Ribas-Ribas, M., Russell, B. C., Stinchcombe, M. C., Tynan, E. and Richier, S. (2016). Production of dissolved organic carbon by Arctic plankton communities: Responses to elevated carbon dioxide and the availability of light and nutrients. Deep-Sea Research Part II 127, 60–74. doi:10.1016/j.dsr2.2016.01.002.
Daniels, C. J., Poulton, A. J., Young, J. R., Esposito, M., Humphreys, M. P., Ribas Ribas, M., Tynan, E. and Tyrrell, T. (2016). Species-specific calcite production reveals Coccolithus pelagicus as the key calcifier in the Arctic Ocean. Marine Ecology Progress Series 555, 29–47. doi:10.3354/meps11820.
Richier, S., Achterberg, E. P., Humphreys, M. P., Poulton, A. J., Suggett, D. J., Tyrrell, T. and Moore, C. M. (2018). Geographical CO2 sensitivity of phytoplankton correlates with ocean buffer capacity. Global Change Biology 24, 4438-4452. doi:10.1111/gcb.14324.

Charismatic megafauna

The polar oceans are a joy to sail through and we often came across whales, penguins in the south and polar bears in the north. In particular, we had this remarkable encounter with a family of polar bears in the sea ice off Greenland:

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