SEA SURFACE TEMPERATURE PREFERENCES OF DENTOGLOBIGERINA ALTISPIRA DURING THE LATE PLIOCENE

The planktic foraminiferal species Dentoglobigerina altispira is common within low-latitude Pliocene assemblages. It became extinct during the late Pliocene, and without an extant descendant, its environmental preferences cannot be calibrated to modern ocean conditions. Instead, its environmental preferences have been gleaned from its negative δ¹⁸O values relative to other taxa, and its geographic distribution, which is most abundant in tropical regions. As such, it is generally considered to be a surface dweller with affinities for warm water and has been grouped with similarly described species for use in Pliocene sea surface temperature (SST) reconstructions. We test the assumption of SST preference during the 3.264 to 3.025 Ma interval using the alkenone paleotemperature index at 17 North Atlantic sites with paired quantitative faunal abundance data and alkenone analyses. Despite published ages of the last occurrence of D. altispira within this interval, our data at all sites indicate its last occurrence to be essentially synchronous at ~2.95 Ma. Direct comparison of D. altispira abundance with alkenone paleotemperature estimates identify this species’ temperature preferences, thereby eliminating the requirement for either extant descendants or comparisons to extant species in determining the optimal SST range. Our results show that during the late Pliocene, the abundance of D. altispira increased with temperature. Maximum abundances occurred in samples with SST estimates >25°C, not unlike the response exhibited by the extant Trilobatus sacculifer. Thus, our data provide additional evidence that this species was a tropical, warm surface water dweller, which supports previous studies that grouped D. altispira with T. sacculifer. It is important to remember, however, that attempts to reconstruct a single environmental variable, like SST, are oversimplifications of complex environmental variables controlling foraminifer abundance and distribution. While temperature is a first-order control, many other factors (e.g. productivity, salinity, nutrients) also play a role.