Beschreibung: The Indonesian Throughflow (ITF), as the sole low-latitude conduit connecting the Pacific and Indian Oceans, regulates the thermohaline balance between these oceans. Investigating the spatio-temporal variability of the ITF and its relationship to precessional forcing is, thus, crucial for understanding the drivers of tropical climate change. Here, we reconstruct the history of the ITF over the past ~120 kyr, based on high resolution (~400 yr) δ18O and Mg/Ca records of Globigerinoides ruber and Pulleniatina obliquiloculata from Core SO217-18540 retrieved from the Flores Sea upwelling region within the main pathway of the ITF. Comparison of these new records with published paleo-oceanographic and climatological data from the western tropical Pacific suggests that annual mean conditions in the Flores Sea were controlled by the ITF rather than by monsoonal upwelling. Our results further indicate that precessional insolation was a major forcing for the hydrological evolution of the ITF during the past 120 kyr. We suggest that precessional insolation forcing paced ITF variability by modulating the mean state of El Niño-Southern Oscillation-like conditions and latitudinal shifts or expansion/contraction of the Intertropical Convergence Zone.

Beschreibung: The Intertropical Convergence Zone (ITCZ), which is the heaviest rain belt on Earth, significantly influences global hydroclimate change and livelihood of nearly 40% of the global population. However, long-term precipitation records are sparse from the Indo-Pacific region, especially from the southern margin of the Indo-Pacific ITCZ, restricting our understanding of the overall natural variability of the ITCZ in the past. In this study, we present a new summer monsoonal precipitation record that spans the last 410 kyr from the southern margin of the Indo-Pacific ITCZ, based on the logarithmic ratio between terrigenous fraction K and pelagic fraction Ca (ln(K/Ca)). Contents of the both elements were derived from X-ray fluorescence scanning on sediment cores from Site U1483 (13°05.24′ S, 121°48.25′ E, water depth 1733 m) that was drilled offshore northwestern Australia during International Ocean Discovery Program Expedition 363. Comparison of the new precipitation record with published precipitation records from the northern margin and meteorological centre of the Indo-Pacific ITCZ shows that precipitation changed nearly in phase between the hemispheres on the precession band, possibly linked to expansion and contraction in the latitudinal extent of the Indo-Pacific ITCZ. In contrast, interhemispheric precipitation was nearly in anti-phase on the obliquity band, likely due to latitudinal migration of the Indo-Pacific ITCZ. Our findings imply that tropical hydroclimate cycles were regulated by the orbital forcing but with significantly different response to changes of the ITCZ on precession and obliquity bands.

Beschreibung: Ocean acidification is predicted to affect marine ecosystems in many ways, including modification of fish behaviour. Previous studies have identified effects of CO2-enriched conditions on the sensory behaviour of fishes, including the loss of natural responses to odours resulting in ecologically deleterious decisions. Many fishes also rely on hearing for orientation, habitat selection, predator avoidance and communication. We used an auditory choice chamber to study the influence of CO2-enriched conditions on directional responses of juvenile clownfish (Amphiprion percula) to daytime reef noise. Rearing and test conditions were based on Intergovernmental Panel on Climate Change predictions for the twenty-first century: current-day ambient, 600, 700 and 900 µatm pCO2. Juveniles from ambient CO2-conditions significantly avoided the reef noise, as expected, but this behaviour was absent in juveniles from CO2-enriched conditions. This study provides, to our knowledge, the first evidence that ocean acidification affects the auditory response of fishes, with potentially detrimental impacts on early survival.