Abstract. Planktonic foraminifera preserved in marine sediments archive the physical and chemical conditions under which they built their shells. To interpret the paleoceanographic information contained in fossil foraminifera, the recorded proxy signals have to be attributed to the habitat and life cycle characteristics of individual species. Much of our knowledge on habitat depth is based on indirect methods, which reconstruct the depth at which the largest portion of the shell has been calcified. However, habitat depth can be best studied by direct observations in stratified plankton nets. Here we present a synthesis of living planktonic foraminifera abundance data in vertically resolved plankton net hauls taken in the eastern North Atlantic during 12 oceanographic campaigns between 1995 and 2012. Live (cytoplasm-bearing) specimens were counted for each depth interval and the vertical habitat at each station was expressed as average living depth (ALD). This allows us to differentiate species showing an ALD consistently in the upper 100 m (e.g., Globigerinoides ruber white and pink), indicating a shallow habitat; species occurring from the surface to the subsurface (e.g., Globigerina bulloides, Globorotalia inflata, Globorotalia truncatulinoides); and species inhabiting the subsurface (e.g., Globorotalia scitula and Globorotalia hirsuta). For 17 species with variable ALD, we assessed whether their depth habitat at a given station could be predicted by mixed layer (ML) depth, temperature in the ML and chlorophyll a concentration in the ML. The influence of seasonal and lunar cycle on the depth habitat was also tested using periodic regression. In 11 out of the 17 tested species, ALD variation appears to have a predictable component. All of the tested parameters were significant in at least one case, with both seasonal and lunar cyclicity as well as the environmental parameters explaining up to > 50 % of the variance. Thus, G. truncatulinoides, G. hirsuta and G. scitula appear to descend in the water column towards the summer, whereas populations of Trilobatus sacculifer appear to descend in the water column towards the new moon. In all other species, properties of the mixed layer explained more of the observed variance than the periodic models. Chlorophyll a concentration seems least important for ALD, whilst shoaling of the habitat with deepening of the ML is observed most frequently. We observe both shoaling and deepening of species habitat with increasing temperature. Further, we observe that temperature and seawater density at the depth of the ALD were not equally variable among the studied species, and their variability showed no consistent relationship with depth habitat. According to our results, depth habitat of individual species changes in response to different environmental and ontogenetic factors and consequently planktonic foraminifera exhibit not only species-specific mean habitat depths but also species-specific changes in habitat depth.
We analyse the dynamics of Indonesian waters using the results of a set of 13 time-slice experiments simulated by the CCSM3-DGVM model. The experiments were carried out to study global climate variability between and within the Quaternary interglacials of Marine Isotope Stages (MIS) 1, 5, 11, 13, and 15. During boreal summer (June-July-August-September), in most of Indonesia, seasonal surface temperature anomalies can largely be explained by local insolation anomalies induced by the astronomical forcing. However, for some time slices, climate feedbacks may modify the surface temperature response in Indonesia, most pronounced in open water close to the Indian and Pacific Oceans. The warmest boreal summer sea-surface temperature (SST) anomaly compared to Pre-Industrial (PI) conditions of up to 1 K was found in the Banda Sea at 125 ka (MIS 5) and 579 ka (MIS 15). The coolest boreal summer SST anomaly down to –2 K at 495 ka (MIS 13) is equally distributed in Indonesian waters. During boreal winter, most of the moderate cooling over large portions of the land and the waters of Indonesia is also associated with local insolation. The most interesting finding in this study, a dipole and tripole precipitation pattern with up to 3.6 mm/day of rainfall anomaly during boreal summer is identified in the western part of the Indonesian waters, Indian Ocean to Banda Sea, and the eastern part of Indonesian waters. The results of this study are expected to be used as basic information to predict the climate in Indonesia for the present and future. This may add to the assessment provided by the IPCC for a better understanding of future climate change in the region, which is a prerequisite for alleviating its impacts.
