Planktonic foraminifera shell fluxes from a weekly resolved sediment trap record in the southwestern Atlantic: Evidence for synchronized reproduction

Abstract

Abstract The reproductive behavior of planktonic foraminifera is an important variable for the interpretation of paleoproxies based on their shells and for the understanding of the role of these organisms in oceanic carbonate flux. Observations from plankton tows have initially provided evidence for the existence of reproductive cycles synchronized with lunar phases in several species. However, subsequent observations from sediment traps yielded inconclusive results. Here we report shell flux data of four key species of planktonic foraminifera (Trilobatus sacculifer, Globigerinoides ruber, Orbulina universa and Neogloboquadrina dutertrei) from multiple deployments of a high-resolution (3-7 days) sediment trap in the southwestern Atlantic. Despite the potential bias related to lateral advection at the shallow deployment depths of the traps, the unusually high sampling resolution makes it possible to better constrain the short-term (lunar) dynamics of shell flux than most previous studies. Using periodic regression on the high-resolution series, we detected for all species evidence for a single flux maximum during one lunar cycle, occurring approximately 4-6 days after the full moon. In this series, 44-52 % of the shell flux in the deep (100 m) trap occurred during the last quarter. Different flux behavior between the shallow (50 m) and the deep (100 m) traps co-located on the same mooring revealed evidence for migration to deeper levels prior to reproduction in T. sacculifer. Although a monthly peak in shell flux was observed in the 3-day resolution deployment, its signature disappeared when all deployments were analyzed together. This analysis still reveals an elevated flux during the last quarter of the lunar cycle, but it seems that the period of the reproductive cycle is not fixed in time. Combined with aliasing at the sampling resolution of 5-7 days, this variable timing overwhelms the strictly periodic component of the shell flux series. We conclude that planktonic foraminifera shell flux and thus the carbonate export to the seafloor is affected by periodicity in the lunar band, but that reproduction does not seem to occur at exactly the same day of the lunar cycle in each month.