Does carbonate ion control planktonic foraminifera shell calcification in upwelling regions?

Planktonic foraminifera shell weights have been recognized as possible proxy for surface water carbonate ion concentration CO₃ and atmospheric CO₂. However, to utilize this proxy, it is important to understand whether shell weights truly reflect surface water CO₃. We utilize shell weights of Globigerina bulloides and Globigerinoides ruber in the size range of 300 to 355 µm from a sediment core recovered from above the lysocline in the upwelling region of western Arabian Sea. Shell weights of G. ruber and G. bulloides show significant correlation with their shell size from recent to 16 kyr, which suggests that shell calcification was controlled by optimum growth conditions. On the other hand, during 16 to 22 kyr, there is no correlation between shell weights and shell size. However, shell weights of G. bulloides exhibit significant negative correlation with annual sea surface temperature which suggests that G. bulloides calcification might have been controlled by surface water CO₃. Therefore it is suggested here that shell weights of G. ruber and G. bulloides cannot be utilized to reconstruct surface water CO₃ in this region.

Uranium in aragonitic marine bivalve shells

Uranium concentrations in foraminiferal and coral skeletons track oceanic [CO₃^2-] and can be useful as a proxy of ocean acidification, but this pH proxy is yet to be investigated in bivalves. Two Saxidomus giganteus shells from the industrialized Puget Sound (WA, USA) and one from the more pristine Kodiak Island (AK, USA) were sampled through ontogeny for U/Ca using laser ablation inductively coupled mass spectrometry. All three shells show a similar pattern of seasonal U/Ca cycles during the first six years of life, followed by a sharp decrease to below the detection limit for the remainder of the clams life (10–20 years), consistent with a biological or ontogenic forcing (vital effect). However, analyzes along a growth-line (carbonate formed at the same time) shows a decrease in U/Ca from the outside of the shell toward the inside, consistent with diagenesis. Clearly U/Ca is not under environmental control in these aragonite shells, but the cause of the variability is not currently clear.

The threat of carbon emissions on the world’s oceans

As the republican presidential primary race drags on, the politics of global warming seem ever more divorced from scientific reality. The process of scientific inquiry, meanwhile, offers yet more warnings about what might happen if fractured climate politics stymie long-term action.

Emitting massive amounts of carbon dioxide doesn’t just change the chemistry of the atmosphere; it makes the oceans more acidic. Predicting the impact on ocean ecosystems involves educated speculation, which often involves applying evidence of what has happened before. In the latest edition of the journal Science, a team of researchers reckons that today’s human-emitted CO2 is increasing ocean acidity far faster than previous, naturally occurring episodes scientists have studied, which themselves appear to have had very alarming results.