drugs alcohol dating violence - Radiocarbon dating of alkenones from marine sediments

According to a study that compared observed water column temperatures with alkenone-based temperatures calculated from surface sediments of the central Pacific Ocean, alkenone-based temperatures in the mid-latitudes are consistent with thermocline temperatures (Ohkouchi et al. Another study also suggested that alkenone-based temperatures represent thermocline temperatures because alkenone concentrations were high at the subsurface in the water column of the central Pacific Ocean (Lee and Schneider ) investigated the vertical distribution of the alkenone concentration in the OT.

In Section 5, we review glacial–interglacial changes in the surface hydrography of the OT and their paleoclimatological implications. Ash layers, including the Kikai-Akahoya (K-Ah) and the Aira-Tanzawa (AT), were found in cores DGKS9603 and MD98-2195.

The K-Ah and AT tephra are likely related to eruptions of the Kikai volcano (7.3 cal ky BP) and the Aira volcano (26–29 cal ky BP), respectively (Machida .

In addition, current SSTs (Japan Oceanographic Data Center dataset from 1906 to 2003) were compared with core-top sediment temperatures reconstructed using the proxies.

Temperatures calculated using the alkenone unsaturation index represent annual mean SSTs, and temperatures calculated using Mg/Ca of capture summer to autumn (June–November) SSTs.

The planktonic foraminiferal assemblage technique does not appear to be promising with respect to accurately reconstructing past SSTs (especially winter) in the OT.

Habitat depth may not be an issue because both alkenone producers and live at the upper surface mixed layer in the area.

As the reconstruction of past SSTs from alkenone, Mg/Ca, and GDGT is based on the information recorded in marine organisms such as coccolithophores, foraminifera, and , knowledge on the habitat depth and seasonal abundance of these organisms is relevant.

It is essential to accurately determine what depth and season are represented by the temperatures estimated using these proxies.

Some previous studies have suggested that the alkenone-based temperature might represent the annual mean SST (Yu et al.

Mg/Ca ratio temperature is thought to represent summer or warm season SSTs.

Glacial–interglacial changes in the surface hydrography of the OT reconstructed based on the SST and salinity proxies were also reviewed here.

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