Sedimentology and geochemistry of late glacial and Holocene sediments from Laguna Potrok Aike, Patagonia

A high-resolution multiproxy geochemical approach was applied to the sediments of Laguna Potrok Aike in an attempt to reconstruct moist and dry periods during the past 16 000 years in southeastern Patagonia. The age-depth model is inferred from AMS 14C dates and tephrochronology, and suggests moist conditions during the Lateglacial and early Holocene (16 000-8700 cal. BP) interrupted by drier conditions before the beginning of the Holocene (13 200-11 400 cal. BP). Data also imply that this period was a major warm phase in southeastern Patagonia and was approximately contemporaneous with the Younger Dryas chronozone in the Northern Hemisphere (12 700-11 500 cal. BP). After 8650 cal. BP a major drought may have caused the lowest lake level of the record. Since 7300 cal. BP, the lake level rose and was variable until the 'Little Ice Age', which was the dominant humid period after 8650 cal. BP.

Planktonic foraminifera and stable isotopic record of sediments from the east Sea of Korea

Foraminiferal assemblage and stable isotopic data are presented for three Quaternary piston cores from Ulleung Basin, East Sea of Korea ((ESK) Japan Sea) near the Korean Peninsula. Major changes in both temperature and salinity strongly affected surface and deep waters of the ESK during the transition from the Last Glacial Maximum (LGM) to the middle Holocene. Local environmental effects dominated during the LGM and the Bølling/Allerød (B/A) when the ESK became semi-isolated from the Pacific Ocean. Regional/global influences dominated following the B/A, after sufficient reconnection with the Pacific. This is reflected in the foraminiferal d18O record which was largely salinity-controlled before the Younger Dryas (YD) and temperature-controlled after the YD. Paleoceanographic changes in the ESK during the last deglaciation reflect sequential reconnection with the Pacific Ocean, through gateways, first (B/A) in the north (Tsugaru Strait) and later (Holocene) in the south (Korea Strait).

Primary production and chlorophyll a in waters of the Kara Sea in September 2007

These studies were performed from September 10 to 29, 2007 in the Kara Sea in transects westward of the Yamal Peninsula, near the St. Anna Trough, in the Ob River estuary (Obskay Guba), and on the adjacent shelf. Concentration of chlorophyll a in the euphotic layer varied from 0.02 to 4.37 µg/l, aver. 0.76 µg/l. Primary production in the water column varied from 10.9 to 148.0 mg C/m**2/day (aver. 56.9 mg C/m**2/day). It was shown that frontal zones divided the Kara Sea into distinct areas with different productivities. Maximum levels of primary production were measured in the deep part of the Yamal transect (132.4 mg C/m**2/day) and the shallow Kara Sea shelf near the Ob River estuary (74.9 mg C/m**2/day). Characteristics of these regions were low salinity of the surface water layer (19-25 psu) and elevated silicon concentration (12.8-28.1 µg-atom/l). It is explainable by river runoff. Frontal zones of the Yamal current within the Yamal and Ob transects showed high assimilation numbers reached to 2.32 and 1.49 mg C/mg Chl/hr, respectively; they were maximal for studied areas.

Mineralogy of sediment cores from the continental slope of Chile

Marine sediment cores from the continental slope off mid-latitude Chile (33°S) were studied with regard to grain-size distributions and clay mineral composition. The data provide a 28,000-yr14C accelerator mass spectrometry-dated record of variations in the terrigenous sediment supply reflecting modifications of weathering conditions and sediment source areas in the continental hinterland. These variations can be interpreted in terms of the paleoclimatic evolution of mid-latitude Chile and are compared to existing terrestrial records. Glacial climates (28,000-18,000 cal yr B.P.) were generally cold-humid with a cold-semiarid interval between 26,000 and 22,000 cal yr B.P. The deglaciation was characterized by a trend toward more arid conditions. During the middle Holocene (8000-4000 cal yr B.P.), comparatively stable climatic conditions prevailed with increased aridity in the Coastal Range. The late Holocene (4000-0 cal yr B.P.) was marked by more variable paleoclimates with generally more humid conditions. Variations of rainfall in mid-latitude Chile are most likely controlled by shifts of the latitudinal position of the Southern Westerlies. Compared to the Holocene, the southern westerly wind belt was located significantly farther north during the last glacial maximum. Less important variations of the latitudinal position of the Southern Westerlies also occurred on shorter time scales.

Sea-surface tempertaure reconstruction of sediment cores from the Southeast Pacific

Applying the alkenone method, we estimated sea-surface temperatures (SSTs) for the past 33 kyr in two marine sediment cores recovered from the continental slope off mid-latitude Chile. The SST record shows an increase of 6.7°C from the last ice age (LIA) to the Holocene climatic optimum, while the temperature contrast between LIA and modern temperatures is only about 3.4°C. The timing and magnitude of the last deglacial warming in the ocean correspond to those observed in South American continental records. According to our SST record, the existence of a Younger Dryas equivalent cooling in the Southeast Pacific is much more uncertain than for the continental climate changes. A warming step of about 2.5°C observed between 8 and 7.5 cal kyr BP may have been linked to the early to mid-Holocene climatic transition (8.2-7.8 cal kyr BP), also described from equatorial Africa and Antarctica. In principal, variations in the latitudinal position of the Southern Pacific Westerlies are considered to be responsible for SST changes in the Peru-Chile current off mid-latitude Chile.

Age determinations and sedimentology on cores GIK17940 and 184-1144

Sedimentological, geochemical and paleomagnetic records were employed to reconstruct the history of East Asian Monsoon variability in the South China Sea (SCS) on orbital- and millennial-to-sub-decadal time scales. A detailed magnetostratigraphy for the southern central SCS was established as well as a stable isotope stratigraphy for ODP Site 1144 for the last 1.2 million years in the northern South China Sea. Furthermore a volcanic tephra layer from the southern central SCS could be identified as the Youngest Toba Ash, which thus re-presents an important age marker and was used to reconstruct paleo wind directions during the eruption 74 ka. Special attention was paid to the high- and ultrahigh-frequency variability in the last glacial-interglacial cycle and the Holocene, and to a precise age control of climate changes in general.

Sedimentology and stable oxygen isotope record of the northern South China Sea

High-resolution sediment records from the South China Sea reveal a winter monsoon dominated glacial regime and a summer monsoon dominated Holocene regime during the last glacial cycle. A fundamental change between regimes occurred during deglaciation through a series of millennial reoccurrences of century-scale changes in the East Asian monsoon (EAM) climate. These abrupt events centered at 17.0, 15.9, 15.5, 14.7, 13.5, 13.9, 13.3, 12.1, 11.5, and 10.7 14C ka correlate well with the millennial-scale events in the Santa Barbara Basin and the Arabian Sea, i.e. a relationship between EAM and El Niño/Southern Oscillation systems. The abrupt increases in summer monsoon imply enhanced heat transport from low-latitude sea area to the midlatitude/high-latitude land area. The phase relationship between events of EAM and ice sheet may reflect a faster EAM response and a slower ice sheet response to the insolation change. A far-reaching conclusion is that the EAM might have triggered the Northern Hemisphere deglaciation.

Sedimentology of the Vietnam shelf

On the Vietnam Shelf more than 1000 miles of shallow high-resolution seismics were analyzed to unravel post-glacial evolution in a tropical, siliciclastic environment together with 25 sediment cores from water depths between 21 and 169 m to determine stratigraphy, distribution and style of sedimentation. Fourty-seven samples were dated with the AMS-14C technique. The shelf was grouped into three regions: a southern part, a central part, and a northern part. On the broad Southern Shelf, sedimentation is influenced by the Mekong River, which drains into the SCS in this area. Here, incised valley fills are abundant that were cut into the late Pleistocene land surface by the Paleo-Mekong River during times of sea level lowstand. Those valleys are filled with transgressive deposits. The Holocene sedimentation rate in this low gradient accommodation-dominated depositional system is in the range of 5-10 and 25-40 cm/ky at locations sheltered from currents. The Central Shelf is narrow and the sedimentary strata are conformable. Here, numerous small mountainous rivers reach the SCS and transport large amounts of detrital sediment onto the shelf. Therefore, the Holocene sedimentation rate is high with values of 50-100 cm/ky in this supply-dominated depositional system. The broad Northern Shelf in the vicinity of the Red River Delta shows, as on the Southern Shelf, incised valleys cut into the Pleistocene land surface by paleo river channels. In this accommodation-dominated shelf area, the sedimentation rate is low with values of 5-10 cm/ky. Where applicable, we assigned the sampled deposits to different paleo-facies. The latter are related to certain intervals of water depths at their time of deposition. Comparison with the sea-level curve of (Hanebuth et al., 2000, doi:10.1126/science.288.5468.1033) indicates subsidence on the Central Shelf, which is in agreement with the high sedimentation rates in this area. In contrast, data from the Northern Shelf suggest tectonic uplift that might be related to recent tectonic movements along the Ailao Shan-Red River Fault zone. Data from the Southern Shelf are generally in agreement with the sea-level curve mentioned above.