ALBERT

Description: The Antarctic Intermediate Water (AAIW) is a key player in global-scale oceanic overturning processes and an important conduit for heat, fresh water, and carbon transport. The AAIW past variability is poorly understood mainly due to the lack of sedimentary archives at intermediate water depths. We present records of benthic stable isotopes from sediments retrieved with the seafloor drill rig MARUM-MeBo at 956 m water depth off northern Chile (GeoB15016, 27°29.48'S, 71°07.58'W) that extend back to 970 ka. The sediments at this site are presently deposited at the boundary between AAIW and Pacific Deep Water (PDW). For previous peak interglacials, our results reveal similar benthic d13C values at site GeoB15016 and of a newly generated stack of benthic d13C from various deep Pacific cores representing the "average PDW." This suggests, unlike today, the absence of AAIW at the site and the presence of nearly pure PDW. In contrast, more positive d13C values at site GeoB15016 compared to the stack imply a considerable AAIW contribution during cold phases of interglacials and especially during glacials. Besides, we used three short sediment cores to reconstruct benthic d13C values from the AAIW core during the last glacial and found a d13C signature similar to today's. Assuming that this was the case also for the past 970 kyr, we demonstrate that sea level changes and latitudinal migrations of the AAIW formation site can only account for about 50% of the full range of past d13C increases at site GeoB15016 during cold periods. Other processes that could explain the remaining of the positive d13C anomalies are increases in glacial AAIW production and/or deeper convection of the AAIW with respect to preceding interglacials.

Description: Logging was performed with the sea floor drill rig MARUM-MeBo70 in a borehole drilled with a 103 mm diameter bit. The 1460 Slimhole Memory SGR instrument developed by ANTARES Datasystems GmbH was used. A CsI(Na) crystal with outer diameter of 37 mm and 250 mm length is used as detector. The probe provides Natural Gamma Ray counts and analyses the spectrum for the concentrations of the natural gamma ray emitters potassium, thorium and uranium with an accuracy of about 10%. The probe was deployed in the memory mode with the logging string being inserted into the drill string and the sensor located about 1.2 m above the drill bit. The measurement was conducted through the drill pipe as upcast while the drill string was pulled back to the seafloor out of the borehole. The trip out speed was about 2 cm/s and the logging frequency was 1 Hz. Data processing was conducted using the Antares software GeoBase5 including an environmental correction compensating for the attenuation of the gamma ray signal by the drill pipe.

Description: Logging was performed with the sea floor drill rig MARUM-MeBo70 in a borehole drilled with a 103 mm diameter bit. The 1460 Slimhole Memory SGR instrument developed by ANTARES Datasystems GmbH was used. A CsI(Na) crystal with outer diameter of 37 mm and 250 mm length is used as detector. The probe provides Natural Gamma Ray counts and analyses the spectrum for the concentrations of the natural gamma ray emitters potassium, thorium and uranium with an accuracy of about 10%. The probe was deployed in the memory mode with the logging string being inserted into the drill string and the sensor located about 1.2 m above the drill bit. The measurement was conducted through the drill pipe as upcast while the drill string was pulled back to the seafloor out of the borehole. The trip out speed was about 2 cm/s and the logging frequency was 1 Hz. Data processing was conducted using the Antares software GeoBase5 including an environmental correction compensating for the attenuation of the gamma ray signal by the drill pipe.

Description: Logging was performed with the sea floor drill rig MARUM-MeBo70 in a borehole drilled with a 103 mm diameter bit. The 1460 Slimhole Memory SGR instrument developed by ANTARES Datasystems GmbH was used. A CsI(Na) crystal with outer diameter of 37 mm and 250 mm length is used as detector. The probe provides Natural Gamma Ray counts and analyses the spectrum for the concentrations of the natural gamma ray emitters potassium, thorium and uranium with an accuracy of about 10%. The probe was deployed in the memory mode with the logging string being inserted into the drill string and the sensor located about 1.2 m above the drill bit. The measurement was conducted through the drill pipe as upcast while the drill string was pulled back to the seafloor out of the borehole. The trip out speed was about 2 cm/s and the logging frequency was 1 Hz. Data processing was conducted using the Antares software GeoBase5 including an environmental correction compensating for the attenuation of the gamma ray signal by the drill pipe.

Description: Logging was performed with the sea floor drill rig MARUM-MeBo70 in a borehole drilled with a 103 mm diameter bit. The 1460 Slimhole Memory SGR instrument developed by ANTARES Datasystems GmbH was used. A CsI(Na) crystal with outer diameter of 37 mm and 250 mm length is used as detector. The probe provides Natural Gamma Ray counts and analyses the spectrum for the concentrations of the natural gamma ray emitters potassium, thorium and uranium with an accuracy of about 10%. The probe was deployed in the memory mode with the logging string being inserted into the drill string. The measurement was conducted as upcast by hooking up the probe inside the drill string with a wire. The trip out speed was about 3 cm/s and the logging frequency was 1 Hz. Data processing was conducted using the Antares software GeoBase5 including an environmental correction compensating for the attenuation of the gamma ray signal by the drill pipe.