ALBERT

Description: Samples were collected during the months of March, April, and May. Measuring the length (C), width (L), height (A), length of aperture (Ca) and width of aperture (La).

Description: Paleoceanographic reconstructions from the Brazil Current are scarce and lack the required temporal resolution to appropriately represent its variability during key periods of the last glacial-interglacial cycles. Here, we present the first high-temporal resolution multiproxy reconstruction of the Brazil Current at 24 °S covering the last 185 ka. During the last and penultimate glacial periods, our Mg/Ca-derived sea surface temperature (SST) record shows a strong cooling at ca. 47 and ca. 156 ka, respectively, that is followed by a warming trend from late-Marine Isotope Stage (MIS) 3 to MIS 1 and from late-MIS 6 to MIS5e, respectively. Importantly, the Brazil Current warmed uninterruptedly towards Termination I (II) after the low SST at ca. 47 and ca. 156 ka, with no SST minima during the Last Glacial Maximum or penultimate glacial maximum. The reason for the strong cooling and the warming trend during late-MIS 3 and late-MIS 6 could reside in the favorable obliquity configuration. However, this mechanism is not sufficient to sustain the warming observed for the rest of the last and penultimate glacial periods. We propose that the change in the Atlantic meridional overturning circulation (AMOC), as described in the literature, from a 'warm' to a 'cold mode' for MIS 2 and MIS 6 is responsible for the accumulation of warm waters in the subtropical western South Atlantic, preventing SST minima during the last and penultimate glacial maxima in the region. Change in benthic d13C corroborates that a fundamental modification in the AMOC mode might have triggered the heat accumulation. Our data also show a sudden increase in SST and surface salinity during the last glacial descent (MIS 4), indicating that the western portion of the subtropical gyres may have acted as a heat and salt reservoir, while higher latitude climates transited to a glacial background. Our findings imply that the AMOC 'cold mode' induces heat storage in the subtropical western South Atlantic and, because of that, the last two regional SST minima occurred out-of-phase with the glacial maxima of higher latitudes.

Description: Model output of the intermediate complexity climate model CLIMBER-2 over the past 5 million years. The simulations were forced with insolation data (O), insolation and land ice data (OI), insolation and carbon dioxide data (OC) and with insolation, land ice and carbon dioxide data (OIC). Sheet 1 contains the main results: northern hemispheric (30-90 deg N), southern hemispheric (30-90 deg S) and global temperatures. Sheet 2 contains the land ice and carbon dioxide forcing in terms of globally averaged radiative forcing. Details are given in the publication. More information or data can be obtained by contacting L.B. Stap (lennert.stap@awi.de).

Description: Aim: To quantify the influence of past archipelago configuration on present-day insular biodiversity patterns, and to compare the role of long-lasting archipelago configurations over the Pleistocene to configurations of short duration such as at the Last Glacial Maximum (LGM) and the present-day. Location: 53 volcanic oceanic islands from 12 archipelagos worldwide - Azores, Canary Islands, Cook Islands, Galápagos, Gulf of Guinea, Hawaii, Madeira, Mascarenes, Pitcairn, Revillagigedo, Samoan Islands, and Tristan da Cunha. Time period: The last 800 Kyr, representing the nine most recent glacial-interglacial cycles. Major taxa studied: Land snails and angiosperms. Methods: Species richness data for land snails and angiosperms were compiled from existing literature and species checklists. We reconstructed archipelago configurations at the following sea-levels: the present-day high interglacial sea-level, the intermediate sea-levels that are representative of the Pleistocene, and the low sea-levels of the LGM. We fitted two alternative linear mixed models for each archipelago configuration on the number of single-island endemic, multiple-island endemic, and native non-endemic species. Model performance was assessed based on the goodness-of-fit of the full model, the variance explained by archipelago configuration, and model parsimony. Results: Single-island endemic richness in both taxonomic groups was best explained by intermediate palaeo-configuration (positively by area change, and negatively by palaeo-connectedness), whereas non-endemic native species richness was poorly explained by palaeo-configuration. Single-island endemic richness was better explained by intermediate archipelago configurations than by the archipelago configurations of the LGM or present-day. Main conclusions: Archipelago configurations at intermediate sea-levels - which are representative of the Pleistocene - have left a stronger imprint on single-island endemic richness patterns on volcanic oceanic islands than extreme archipelago configurations that persisted for only a few thousand years (such as the LGM). In understanding ecological and evolutionary dynamics of insular biota it is essential to consider longer-lasting environmental conditions, rather than extreme situations alone.

Description: It is still an open question how equilibrium warming in response to increasing radiative forcing – the specific equilibrium climate sensitivity S – depends on background climate. We here present palaeodata-based evidence on the state dependency of S, by using CO2 proxy data together with a 3-D ice-sheet-model-based reconstruction of land ice albedo over the last 5 million years (Myr). We find that the land ice albedo forcing depends non-linearly on the background climate, while any non-linearity of CO2 radiative forcing depends on the CO2 data set used. This non-linearity has not, so far, been accounted for in similar approaches due to previously more simplistic approximations, in which land ice albedo radiative forcing was a linear function of sea level change. The latitudinal dependency of ice-sheet area changes is important for the non-linearity between land ice albedo and sea level. In our set-up, in which the radiative forcing of CO2 and of the land ice albedo (LI) is combined, we find a state dependence in the calculated specific equilibrium climate sensitivity, S[CO2,LI], for most of the Pleistocene (last 2.1 Myr). During Pleistocene intermediate glaciated climates and interglacial periods, S[CO2,LI] is on average ~ 45 % larger than during Pleistocene full glacial conditions. In the Pliocene part of our analysis (2.6–5 Myr BP) the CO2 data uncertainties prevent a well-supported calculation for S[CO2,LI], but our analysis suggests that during times without a large land ice area in the Northern Hemisphere (e.g. before 2.82 Myr BP), the specific equilibrium climate sensitivity, S[CO2,LI], was smaller than during interglacials of the Pleistocene. We thus find support for a previously proposed state change in the climate system with the widespread appearance of northern hemispheric ice sheets. This study points for the first time to a so far overlooked non-linearity in the land ice albedo radiative forcing, which is important for similar palaeodata-based approaches to calculate climate sensitivity. However, the implications of this study for a suggested warming under CO2 doubling are not yet entirely clear since the details of necessary corrections for other slow feedbacks are not fully known and the uncertainties that exist in the ice-sheet simulations and global temperature reconstructions are large.

Description: Marine sediment records from the Oligocene and Miocene reveal clear 400,000-year (400-kyr) climate cycles related to variations in orbital eccentricity. These cycles are also observed in the Plio-Pleistocene records of the global carbon cycle. However they are absent in the Late Pleistocene ice-age record over the past 1.5 million years. Here, we present a simulation of global ice volume over the past 5 million years with a coupled system of four 3-D ice-sheet models. Our simulation shows that the 400-kyr long eccentricity cycles of Antarctica vary coherently with d13C records during the Pleistocene suggesting that they drive the long-term carbon cycle changes throughout the past 35 million years. The 400-kyr response of Antarctica is eventually suppressed by the dominant 100-kyr glacial cycles of the large ice sheets in the Northern Hemisphere (NH).

Description: The operator effect is a well-known analytical bias already quantified in some taphonomic studies. However, the influence of operator bias in the replicability on taphonomic studies has still not been considered. Here, we quantified for the first time this bias using different multivariate statistical techniques, testing if the operator effect is related to the replicability. We analyzed the results reported by 15 operators working on the same dataset. Each operator analyzed 30 bioclasts (bivalve shells) by site, from a total of five sites, considering the following taphonomic attributes: shell fragmentation, edge rounding, corrasion, bioerosion, and color alteration. The operator effect followed the same pattern reported in previous studies, characterized by a worse correspondence for those attributes having more than two levels of damage categories. However, the effect did not appear to have relation to replicability, because nearly all operators found differences among sites. The binary attribute bioerosion exhibited 83% of correspondence among operators, but at the same time, it was the taphonomic attribute that showed the highest dispersion among operators (28%). Therefore, we concluded that binary attributes, despite indicating a reduction of the operator effect diminishes replicability, result in different interpretations of concordant data. We found that a variance value of nearly 8% among operators was enough to generate a different taphonomic interpretation, in a Q-mode cluster analysis. The results reported here showed that the statistical method employed influences the level of replicability and comparability of a study and that the availability of results may be a valid alternative to reduce bias.

Description: These photographs of sea ice were taken from the South Africa's polar research vessel, the SA Agulhas II during the 2019 Southern oCean seAsonaL Experiment (SCALE) cruise. Images show various kinds of sea ice found in the marginal ice zone (MIZ). They were taken as a supplementary resource in understanding how in-situ conditions compare to those described by remote-sensed and modelled sea ice data.