Search

Metal/calcium ratios in two long‐lived deep‐sea gorgonian corals (Lepidisis and Corallium spp.) in the Southwest Pacific evidence periodic decadal variability at depths that correspond to Antarctic Intermediate Water (AAIW) and shallow Upper Circumpolar Deep Water, and a shift in the mid‐1930s to late‐1930s in mean ambient temperatures, barium/silicate concentrations and possibly pH, the rate at which these properties change over time, and the relationship between temperatures at fixed depth and the Southern Annular Mode (SAM). The decadal periodicity, which is evident in other biological indices in the study area, can be accounted for by water mass heave on the order of 100–150 m, which is consistent with observed scales of variability in the AAIW. The proximate and ultimate causes of the midcentury shifts are unclear, but could be related to suggested mid‐20th century changes in climate parameters globally and, more specifically, in the subpolar SW Pacific. Plain Language Summary: The dynamics of the Southern Ocean play a critical role in global climate and oceanography, but sparse historical instrumental data make it difficult to assess the significance of recently observed changes. We help fill this information gap by analyzing apparent proxies for ambient temperature, barium/silicate concentrations, and possibly pH in the carbonate skeletons of a pair of very long‐lived deep‐sea corals. The data strongly suggest a previously unreported ∼23‐year periodicity in two Southern Ocean water masses (Antarctic Intermediate Water and Upper Circumpolar Deep Water), which is likely to be the result of vertical shifts in water mass distributions. The long‐term data also suggest the water masses cooled, became less acidic and had declining barium/silicate concentrations from at least the early 1700s until the early to mid‐1900s, after which the sign of the long‐term trends reversed. The causes of the long‐term trends and their reversal are not clear, but may be related to changes to climate parameters globally, but more specifically to those in the SE Pacific, where Antarctic Intermediate Water is formed. Key Points: Three environmental proxies were examined in skeletal composition of long‐lived deep‐water gorgonian corals in the SW PacificThe time series indicate coherent ca. 23‐year periodicity at depths corresponding to the AAIW and UCDWLong‐term trends in all three proxies reversed sign in the early to mid‐1900s, along with their relationship with the SAM [ABSTRACT FROM AUTHOR]

Aim To reconstruct ecological changes from the fossil record of a unique wetland on the tropical oceanic island of Tahiti, between 44.5 and 38 cal. kyr bp. Location Vaifanaura'amo'ora, Tamanu Plateau, Punaru'u Valley, Tahiti, Society Islands, French Polynesia (17°38′S, 149°32′50″E). Methods Fossil pollen, spores, seeds, diatoms and invertebrates were examined from a 3.7 m core consisting of Pleistocene-aged algal sediment overlain by late Holocene peat. Results Between 44.5 and 41.5 cal. kyr bp, Ficus trees, sub-shrubs including Sigesbeckia orientalis L., the C4 grass species Paspalum vaginatum Sw., and extinct Pritchardia palms dominated the Vaifanaura'amo'ora wetland. This vegetation association is no longer present in the tropical oceanic Pacific islands. After 41.5 cal. kyr bp, the climate rapidly became drier and cooler with grasses, sedges and ferns dominating the vegetation. Algal sediment accumulation ceased after 38 cal. kyr bp due to prolonged dry climate conditions recorded across the Pacific Ocean. Sediment accumulation recommenced in the late Holocene. Main conclusions The ecological responses identified from Tahiti provide evidence counter to the prevailing view that the tropical oceans buffered the ecological effects of abrupt climate changes during the last glacial period. [ABSTRACT FROM AUTHOR]

Recent theories for glacial-interglacial climate transitions call on millennial climate perturbations that purged the deep sea of sequestered carbon dioxide via a "bipolar ventilation seesaw." However, the viability of this hypothesis has been contested, and robust evidence in its support is lacking. Here we present a record of North Atlantic deep-water radiocarbon ventilation, which we compare with similar data from the Southern Ocean. A striking coherence in ventilation changes is found, with extremely high ventilation ages prevailing across the deep Atlantic during the last glacial period. The data also reveal two reversals in the ventilation gradient between the deep North Atlantic and Southern Ocean during Heinrich Stadial 1 and the Younger Dryas. These coincided with periods of sustained atmospheric CO2 rise and appear to have been driven by enhanced ocean-atmosphere exchange, primarily in the Southern Ocean. These results confirm the operation of a bipolar ventilation seesaw during deglaciation and underline the contribution of abrupt regional climate anomalies to longer-term global climate transitions. [ABSTRACT FROM AUTHOR]

New radiocarbon and sedimentological results from the Gulf of Alaska document recurrent millennial-scale episodes of reorganized Pacific Ocean ventilation synchronous with rapid Cordilleran Ice Sheet discharge, indicating close coupling of ice-ocean dynamics spanning the past 42,000 years. Ventilation of the intermediate-depth North Pacific tracks strength of the Asian monsoon, supporting a role for moisture and heat transport from low latitudes in North Pacific paleoclimate. Changes in carbon-14 age of intermediate waters are in phase with peaks in Cordilleran ice-rafted debris delivery, and both consistently precede ice discharge events from the Laurentide Ice Sheet, known as Heinrich events. This timing precludes an Atlantic trigger for Cordilleran Ice Sheet retreat and instead implicates the Pacific as an early part of a cascade of dynamic climate events with global impact. [ABSTRACT FROM AUTHOR]