Planktonic Foraminifera are widely used for environmental reconstructions through measurements of their shell’s geochemical characteristics, including its stable oxygen and carbon isotope composition. Using these parameters as unbiased proxies requires a firm knowledge of all potential confounding factors influencing foraminiferal shell geochemistry. One such parameter is the shell calcification intensity (shell weight normalized for shell size) that may influence the shell δ18O value either bioenergetically (by reducing energy available and required for equilibrium isotope fractionation during faster calcification) or kinetically (by influencing calcification depth through the shell’s density contrast with seawater). Specimens from the Globigerinoides ruber/elongatus compound from a sediment trap in the North Atlantic have been used to quantify the influence of shell calcification intensity on shell δ18O values. Shell calcification intensity was found to have a significant effect on the shell stable oxygen isotope composition in all species. Through model fitting, it is suggested that the effect size may be in a range of 1 to 2‰ (depending on species, depth migration, and local oceanographic conditions). We show that the confounding effect of shell calcification intensity on stable oxygen isotope composition can be of importance, depending on the anticipated precision of the derived reconstructions. A framework is provided to quantify this effect in future studies.

Using long-term satellite altimeter data, a new streamline-based algorithm is developed to identify the Kuroshio intrusion types and describe the seasonal variations of related dynamical properties. Results from this new classification show that a mixing of leaping, looping and leaking streamlines is the dominant form of Kuroshio intrusion into the South China Sea (SCS). The leaping path is very stable and crosses the Luzon Strait mainly through the Balintang Channel regardless of seasons, while the streamlines leaking into the SCS is more likely to intrude via the channel between the Babuyan Island and the Camiguin Island. Large seasonal variations are found with the percentage of each kind of streamline and the Luzon Strait Transport (LST), but not with the intensity, width and current axis position of the Kuroshio. The along-streamline analysis reveals that the seasonal intrusion of the Kuroshio is essentially the seasonal variation of the cyclonic shear part of the flow. A possible physical mechanism is proposed to accommodate these seasonal characteristics based on globally the vorticity (torque work) balance between the basin-wide wind stress and the lateral friction, as well as locally the loss of balance between the torques of interior stresses and normal stresses both provided by the wall boundary, together with a plausible conjecture that the seasonally-reversing monsoon can significantly modify the torque of the interior stresses within the cyclonic shear part of the flow and thus responsible for the seasonal variation of the Kuroshio intrusion.