The impact of essential climate variables on respiration rates in subpolar and polar planktonic foraminifera

Abstract. This study investigates the impact of Essential Climate Variables (ECVs) on the respiration rate of polar planktonic foraminifera Neogloboquadrina pachyderma and subpolar Turborotalita quinqueloba and Neogloboquadrina incompta to advance our understanding of foraminifera physiology and geochemical proxy interpretation for species living in understudied subpolar and polar environments. Respiration rates were measured on a total of 166 specimens collected during two field campaigns to the Nordic Seas. To size-normalise respiration rates we measured cavity volume and maximum diameter using x-ray microcomputed tomography (micro-CT) (³√cavity volume = (0.56 (max Ø)−0.38)). Our results show that the physiological response of foraminifera sharing overlapping environments is diverse, with N. pachyderma exhibiting remarkable stability over large gradients in temperature, salinity, carbonate chemistry, dissolved oxygen and nutrients. Conversely, N. incompta and T. quinqueloba have a much stronger thermal response. The difference between species is best described by their respective Q₁₀ (the factor by which the rate of respiration changes with a 10 °C increase in temperature) values of 1.41 for N pachyderma and 3.45 and 4.55 for N. incompta and T. quinqueloba, respectively. We also find a significant relationship between cavity volume and respiration rate (Log₁₀ respiration rate = 0.399 (Log₁₀ cavity volume) − 5.785)) for all three species analysed here, which is consistent with marine protists globally. We conclude that respiration is unlikely to influence geochemical proxies and therefore past climate reconstructions derived from N. pachyderma, however, this may not apply to N. incompta and T. quinqueloba.