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Glacial geologic studies in the Southern Hemisphere (SH) mid-latitudes (40-54°S) indicate renewed glacial activity in southern South America (Patagonia) and New Zealand's (NZ) South Island starting at ∼7 kyr, the so-called neoglaciation. Available data indicate that neoglacial advances in these regions occurred during a rising trend in atmospheric CO and CH concentrations, lower-than-present but increasing summer insolation and seasonality contrasts. In this paper we examine the climatological context in which neoglaciations occurred through analysis of the complete Paleoclimate Modelling Inter-comparison Project (PMIP2) database of simulations at 6 kyr for the SH. We observe that the amplitude of the annual insolation cycle in the SH did not change significantly at 6 kyr compared to the pre-industrial values, the largest difference occurring in autumn (MAM, negative anomalies) and spring (SON, positive anomalies). The simulated changes in temperatures over the SH respond to the insolation changes, with a 1-2 month delay over the oceans. This results in a reduced amplitude of the annual cycle of temperature and precipitation over most continental regions, except over Patagonia and NZ, that show a slight increase. In contrast, large-scale circulation features, such as the low and upper level winds and the subtropical anticyclones show an amplified annual cycle, as a direct response to the increased/decreased insolation during the transitional seasons SON/MAM. In the annual mean, there is a small but consistent equatorward shift of the latitude of maximum wind speed of 1-3° over the entire SH, which results in a small increase of wind speed over the South Pacific and Atlantic Oceans north of ∼50°S and a widespread decline south of 50°S. PMIP2 simulations for 6 kyr, indicate that in the annual mean, the SH mid-latitudes were colder, wetter and with stronger winds north of about 50°S. These conditions are consistent with the observed neoglacial advances in the region, as well as with terrestrial paleoclimate records from Patagonia that indicate cooling and a multi-millennial rising trend in Southern Westerly Wind intensity starting at ∼7.8 kyr. [ABSTRACT FROM AUTHOR]

South Africa's southwestern Cape occupies a critical transition zone between Southern Hemisphere temperate (winter) and tropical (summer) moisture-bearing systems. In the recent geological past, it has been proposed that the relative influence of these systems may have changed substantially, but little reliable evidence regarding regional hydroclimates and rainfall seasonality exists to refine or substantiate the understanding of long-term dynamics. In this paper we present a mid-to late Holocene multi-proxy record of environmental change from a rock hyrax midden from Katbakkies Pass, located along the modern boundary between the winter and summer rainfall zones. Derived from stable carbon and nitrogen isotopes, fossil pollen and microcharcoal, these data provide a high resolution record of changes in humidity, and insight into changes in rainfall seasonality. Whereas previous work concluded that the site had generally experienced only subtle environmental change during the Holocene, our records indicate that significant, abrupt changes have occurred in the region over the last 7000 years. Contrary to expectations based on the site's location, these data indicate that the primary determinant of changes in humidity is summer rather than winter rainfall variability, and its influence on drought season intensity and/or length. These findings are consistent with independent records of upwelling along the southern and western coasts, which indicate that periods of increased humidity are related to increased tropical easterly flow. This substantially refines our understanding of the nature of temperate and tropical circulation system dynamics in SW Africa, and how changes in their relative dominance have impacted regional environments during the Holocene. [ABSTRACT FROM AUTHOR]

The oceans are warming, but it is unclear how marine productivity will be affected under future climate change. In this study we examined a wide range of paleoproductivity proxies along a latitudinal transect (36–58°S) in the SW Pacific during the early Holocene climatic optimum, to explore regional patterns of productivity in a slightly warmer‐than‐present world. During the early Holocene there is a small increase in productivity in the subtropical waters, no change at the subtropical frontal zone, and conflicting evidence in records immediately south of the subtropical front, where an increase is inferred from one core site, but not at the other. Evidence for an increase in productivity in Antarctic Surface Waters, south of the polar front, is also equivocal. We infer a small increase in productivity in subtropical waters, and the ocean just south of the subtropical front was associated with changes in the ocean circulation of the SW Pacific, driven by changes in the Southern Hemisphere Westerly Winds split‐jet structure in this region. The relatively modest warming during the early Holocene climatic optimum in the SW Pacific indicates that this time period may provide an analog for future productivity for the midcentury (2055) under Intergovernmental Panel on Climate Change Representative Concentration Pathway 8.5 or for the end of the century (2100) under Representative Concentration Pathway 4.5. However, higher‐resolution, downscaled models, with realistic Southern Hemisphere Westerly Winds, will be necessary to forecast future productivity for this oceanographically complex region. Key Points: There is evidence for a small increase in productivity in subtropical water and an expanded subtropical frontal region during the early HoloceneThe expansion of the Subtropical Front is likely due to changes in the Southern Hemisphere Westerly Wind split‐jet structureThe early Holocene is not a suitable analog for future productivity for the end of the century Representative Concentration Pathway 8.5 [ABSTRACT FROM AUTHOR]

We report a previously-unexplored natural temperature cycle recorded in ice cores from Antarctica--the Antarctic Centennial Oscillation (ACO)--that has oscillated for at least the last 226 millennia. Here we document the properties of the ACO and provide an initial assessment of its role in global climate. We analyzed open-source databases of stable isotopes of oxygen and hydrogen as proxies for paleo-temperatures. We find that centennial-scale spectral peaks from temperature-proxy records at Vostok over the last 10,000 years occur at the same frequencies (±2.4%) in three other paleoclimate records from drill sites distributed widely across the East Antarctic Plateau (EAP), and >98% of individual ACOs evaluated at Vostok match 1:1 with homologous cycles at the other three EAP drill sites and conversely. Identified ACOs summate with millennial periodicity to form the Antarctic Isotope Maxima (AIMs) known to precede Dansgaard-Oeschger (D-O) oscillations recorded in Greenland ice cores. Homologous ACOs recorded at the four EAP drill sites during the last glacial maximum appeared first at lower elevations nearest the ocean and centuries later on the high EAP, with latencies that exceed dating uncertainty >30-fold. ACO homologs at different drill sites became synchronous, however, during the warmer Holocene. Comparative spectral analysis suggests that the millennial-scale AIM cycle declined in period from 1500 to 800 years over the last 70 millennia. Similarly, over the last 226 millennia ACO repetition period (mean 352 years) declined by half while amplitude (mean 0.67 °C) approximately doubled. The period and amplitude of ACOs oscillate in phase with glacial cycles and related surface insolation associated with planetary orbital forces. We conclude that the ACO: encompasses at least the EAP; is the proximate source of D-O oscillations in the Northern Hemisphere; therefore affects global temperature; propagates with increased velocity as temperature increases; doubled in intensity over geologic time; is modulated by global temperature variations associated with planetary orbital cycles; and is the probable paleoclimate precursor of the contemporary Antarctic Oscillation (AAO). Properties of the ACO/AAO are capable of explaining the current global warming signal. [ABSTRACT FROM AUTHOR]

High-resolution climate reconstructions from a range of natural archives across the world are fundamental to place current climate change into perspective. Paleoclimate records for the Southern Hemisphere are scarce and only a few quantitative high-resolution reconstructions exist for the past millennium. We present a record of annually laminated sediments of Lago Plomo (46°59′S, 72°52′W,203 m a.s.l.) located east of the Northern Patagonian Ice Field (NPI). Radiometric dating (210Pb, 137Cs, 14C AMS) is consistent with counts of millimetre-scale laminae, confirming the annual nature of the laminae couplets with a light summer and a dark winter layer. The varves were analyzed for thickness, mass accumulation rate (MAR), scanning x-ray fluorescence (XRF) and scanning reflectance spectroscopy in the visible range (VIS-RS). MAR data were calibrated against austral winter (JJA) precipitation data (CRU TS 3.0) for the period ad 1930–2002 (r = 0.67, p(aut) < 0.05). Using a linear inverse regression model we reconstructed winter precipitation for Lago Plomo back to ad 1530. The root mean squared error of prediction (RMSEP) is small (13.3 mm/month; 12% of the average precipitation) compared with the pronounced decadal and multidecadal variability, suggesting that most of the reconstructed variability is significant. Wetter phases (reference ad 1930–2002) were observed around ad 1600, ad 1630–1690 and ad 1780–1850, and a prolonged drier period ad 1690–1780 with a multidecadal minimum centered on ad 1770. The spatial correlation for South America suggests that the JJA precipitation record from Lago Plomo is representative for large areas in the southwest between c. 41°S and 51°S. [ABSTRACT FROM AUTHOR]

The Holocene climate is simulated in a 9000-yr-long transient experiment performed with the ECBilt-CLIO-VECODE coupled atmosphere–sea ice–ocean–vegetation model. This experiment is forced with annually varying orbital parameters and atmospheric concentrations of CO2 and CH4. The objective is to study the impact of these long-term forcings on the surface temperature evolution during different seasons in the high-latitude Southern Hemisphere. We find in summer a thermal optimum in the mid-Holocene (6–3 ka BP), with temperatures locally 3°C above the preindustrial mean. In autumn the temperatures experienced a long-term increase, particularly during the first few thousand years. The opposite trend was simulated for winter and spring, with a relatively warm Southern Ocean at 9 ka BP in winter (up to 3.5°C above the preindustrial mean) and a warm continent in spring (+3°C), followed by a gradual cooling towards the present. These long-term temperature trends can be explained by a combination of (1) a delayed response to orbital forcing, with temperatures lagging insolation by 1 to 2 months owing to the thermal inertia of the system, and (2) the long memory of the Southern Ocean. This long memory is related to the storage of the warm late winter–spring anomaly below the shallower summer mixed layer until next winter. Sea ice plays an important role as an amplifying factor through the ice–albedo and ice–insulation feedbacks. Our experiments can help to improve our understanding of the Holocene signal in proxies. For instance, the results suggest that, in contrast to recent propositions, teleconnections to the Northern Hemisphere appear not necessarily to explain the history of Southern Hemisphere temperature changes during the Holocene. [ABSTRACT FROM AUTHOR]