ALBERT

Description: A high-resolution diatom census coupled with other proxy data from Laurentian Fan (LF) provides a detailed description of the last deglaciation, bringing new insight to that period by revealing directly the timing of sea-ice formation and melting. Cold events Heinrich Event 1 (H1) and the Younger Dryas (YD) were multiphase events. H1 (~16.8-15.7 cal kyr BP) was defined by a two-pulse release of icebergs promoting sea-ice formation. Melting of sea-ice after H1 corresponds to a cold and fresh anomaly that may have kept the Bølling colder than the Allerød. At ~13.6 cal kyr BP, a cooling trend culminated with sea-ice formation, marking the YD onset (~12.8 cal kyr BP). The decrease in sea-ice (~12.2 cal kyr BP) led to a YD second phase characterized by very cold winters. However, the contribution of warm water diatoms tends to increase at the same time and the YD gradual end (~11.6 cal kyr BP) contrasts with its abrupt end in Greenland ice cores. The YD cannot be regarded as an event triggered by a fresh water input through the Laurentian Channel since only one weak brief input nearly 1000 yrs after its onset is recorded. Very cold and cool conditions without ice mark the following Preboreal. A northward heat flux between 10.8 and 10.2 cal kyr BP was interrupted by the increased influence of coastal waters likely fed by inland melting. There was no further development of sea-ice or ice-drift then.

Description: To better understand Holocene vegetation and hydrological changes in South Africa, we analyzed pollen and microcharcoal records of two marine sites GeoB8331 and GeoB8323 from the Namaqualand mudbelt offshore the west coast of South Africa covering the last 9900 and 2200 years, respectively. Our data corroborate findings from literature that climate developments apparently contrast between the summer rainfall zone (SRZ) and winter rainfall zone (WRZ) over the last 9900 years, especially during the early and middle Holocene. During the early Holocene (9900-7800 cal.yr BP), a minimum of grass pollen suggests low summer rainfall in the SRZ, and the initial presence of Renosterveld vegetation indicates relatively wet conditions in the WRZ. Towards the middle Holocene (7800-2400 cal. yr BP), a rather moist savanna/grassland rich in grasses suggests higher summer rainfall in the SRZ resulting from increased austral summer insolation and a decline of fynbos vegetation accompanied by an increasing Succulent Karoo vegetation in the WRZ possibly suggests a southward shift of the Southern Hemisphere westerlies. During the last 2200 years, a trend towards higher aridity was observed for the SRZ, while the climate in the WRZ remained relatively stable. The Little Ice Age (ca. 700-200 cal. yr BP) was rather cool in both rainfall zones and drier in the SRZ while wetter in the WRZ.

Description: This study examines climate change impacts (increased temperature and pCO2) on canopy-forming Desmarestia anceps and D. menziesii from the western Antarctic Peninsula during the austral summer–winter of 2013. These are ecologically important species that play a role functionally equivalent to kelp forests in this region. Two-way factorial microcosm experiments with treatments reflecting near-future ocean conditions were run with these species and include increased temperature alone (3.5 °C × pH 8.0), reduced pH alone (1.5 °C × pH 7.6), and both factors combined (3.5 °C × pH 7.6). Phlorotannin concentration, chlorophyll a concentration, growth, and photosynthetic parameters (slope to saturation of photo centers (α), saturating irradiance (E k), maximum electron transport rate (ETRmax), and maximum quantum yield of photosystem II (F v/F m)) were used to assess the physiological responses of the individuals to the different climate change treatments. Few significant impacts were observed: In D. menziesii, E k at the midpoint (after 39 days) was significantly higher in the 3.5 °C × pH 7.6 treatment and phlorotannin concentration was significantly higher in the 1.5 °C × pH 7.6 treatment than others at the end point of the experiment (79 days). All individuals in the experiment grew quickly through the midpoint, but growth declined thereafter. The photosynthetic apparatus of these species acclimated to microcosm conditions, and photo-physiological parameters changed between initial, midpoint, and end point measurements. Results indicate that D. menziesii is the more sensitive of the two species and that climate change factors can have a synergistic effect on this species. However, neither species responds negatively to climate change factors at the level of change used in this study, though the observed shifts in phlorotannin concentration and photosynthetic characteristics may have an unforeseen impact on the community dynamics in this geographic area.