DOI: 10.25921/3jth-d104
title: NOAA/WDS Paleoclimatology - North Atlantic IODP U1308 Middle Pleistocene Heinrich Events Data

description: Heinrich events are well documented for the last glaciation, but little is known about their occurrence in older glacial periods of the Pleistocene. Here we report scanning XRF and bulk carbonate d18O results from Integrated Ocean Drilling Program Site U1308 (reoccupation of Deep Sea Drilling Project Site 609) that are used to develop proxy records of ice-rafted detritus (IRD) for the last ~1.4 Ma. Ca/Sr is used as an indicator of IRD layers that are rich in detrital carbonate (i.e., Heinrich layers), whereas Si/Sr reflects layers that are poor in biogenic carbonate and relatively rich in detrital silicate minerals. A pronounced change occurred in the composition and frequency of IRD at ~640 ka during marine isotope stage (MIS) 16, coinciding with the end of the middle Pleistocene transition. At this time, "Hudson Strait" Heinrich layers suddenly appeared in the sedimentary record of Site U1308, and the dominant period of the Si/Sr proxy shifted from 41 ka prior to 640 ka to 100 ka afterward. The onset of Heinrich layers during MIS 16 represents either the initiation of surging of the Laurentide Ice Sheet (LIS) off Hudson Strait or the first time icebergs produced by this process survived the transport to Site U1308. We speculate that ice volume (i.e., thickness) and duration surpassed a critical threshold during MIS 16 and activated the dynamical processes responsible for LIS instability in the region of Hudson Strait. We also observe a strong coupling between IRD proxies and benthic d13C variation at Site U1308 throughout the Pleistocene, supporting a link between iceberg discharge and weakening of thermohaline circulation in the North Atlantic.
description: Multiproxy Heinrich Events data from IODP core U1308 back to the 
middle Pleistocene.  Individual data series are as follows:  

Tie points: 
Modified splice tie points for composite section of Site U1308. 

Depth-Age: 
Age-depth points used to construct chronology for Site U1308 
Radiocarbon dates are projected into Site U1308 from Site 609 [Bond et al., 1993] 
by matching gray scale records. Ages for the interval from 0 to 1.9 mcd were 
calculated assuming a constant sedimentation rate of 5.37 cm kyr-1 which is 
generally consistent with radiocarbon dates from DSDP Site 609. From 35 to 60 ka, 
the benthic d18O record was correlated to MD95Ð2042 using the SFCP04 time scale 
[Shackleton et al., 2004. Prior to 60 ka, the benthic d18O record was correlated 
to the stacked d18O record of Lisiecki and Raymo [2005]. 

Benthic isotopes:  
Oxygen and carbon isotopes of the benthic foraminifer Cibicoides wuellerstorfi, 
units = per mille relative to VPDB 

Bulk carbonate O18: 
Oxygen isotope values of homogenized bulk sediment, units = per mille relative to VPDB 

Sr XRF: 
Ca/Sr and Si/Sr ratios of counts from core scanning XRF measurements. 
See Hodell et al. (2008) for measurement details and calibration. 

Magnetic susceptibility: 
Magnetic susceptibility measured on u-channels. 
See Hodell et al. (2008) for methods. 

Magnetic susceptibility, shipboard: 
Shipboard magnetic susceptibility on the modified composite splice. 
See Expedition 303 Scientists (2006a,b) for explanation of methods. 

Bulk Density: 
Shipboard bulk density on the modified composite splice. 
See Expedition 303 Scientists (2006a,b) for explanation of methods. 

NGR:  
Shipboard natural gamma radiation on the modified composite splice. 
See Expedition 303 Scientists (2006a,b) for explanation of methods. 

Reflectance:  
Shipboard color reflectance lightness on the modified composite splice. 
See Expedition 303 Scientists (2006a,b) for explanation of methods. 


Core location:
IODP Site U1308 49°52.67'N, 24°14.3'W, Water depth 3883 m