Ultrahigh-resolution records

One of the great successes of ocean drilling has been the continuous increase in the available temporal resolution of sediment core generated climatic proxy data throughout the life times of the Deep Sea Drilling Project (DSDP), ODP, and IODP.

Scientific drilling on land and at sea has played a key role in advancing our knowledge of climate change, for example by helping to demonstrate the effects of orbital variations on climate, by revealing evidence for extreme warm events in the past, by establishing the timing of Antarctic ice growth, and by providing insights into the hydrologic balance of lake systems around the world (Thurow et al., 2009). A recent workshop identified key sediment sections that are available for generating societally relevant high-resolution records with a wide geographical distribution (Thurow et al., 2009; Fig. 2.6);

however, despite some long records in the oceans (e.g., Santa Barbara Basin: Behl and Kennett, 1996; Hendy and Kennett, 2000; Cariaco Basin : Peterson et al., 2000; Hughen et al., 2004) and on land (Scholz et al., 2007; Hodell et al., 2008), high-resolution records generated by scientific coring and drilling is currently limited in both number and global coverage (Voelker, 2002; Clement and Peterson, 2008). Several studies have now shown the possibility to decipher short timescale climate variability by comparing sediment-derived records with ice-core records (Tzedakis et al., 2009). In addition, the synchronization of high-resolution records has recently undergone significant advancements through the application of ultrahigh-resolution correlations of relative magnetic paleo-intensities determined from sediment cores (IODP Expeditions 303/306:

Channell et al., 2004). This method provides a significant new opportunity to fully exploit high- and ultrahigh-resolution records and provides the backbone for new drilling proposals of high societal relevance (e.g., drilling near the West Antarctic ice sheet).

With the aim to better predict the likely manifestation of future climate change, it is critical to better understand the causes and consequences of rapid environmental/climate change at various timescales (annual, interannual, multi-decadal, centennial, millennial, Mitchell, 1976), including societally relevant ultrahigh-resolution,

Figure 2.6 Compilation of potential drilling sites proposed by workshop participants to address the scientific themes ‗Warm intervals through time‘, ‗Ocean-continent interactions‘, ‗Biogeochemical cycles‘,

‗Ecosystem change‘, and ‗Climate Modes‘; from Thurow et al., (2009). Site numbers are linked to information that can be found in Appendix 1 at http://high-resolution.icdp-online.org.

approaching those of instrumental records. Well-dated, well-calibrated sedimentary records (e.g., sediments including varved marine and lacustrine muds, corals, ice cores, speleothems), with sub-annual to centennial resolution spanning different time intervals, provide an unparalleled opportunity to explore past natural climate variability by revealing the details and complexities of the climate system (e.g., better definition of the climate norm and anomalies), and constraining rates and magnitudes of change.

Central to these aims is the acquisition of ultrahigh-resolution and multi-proxy records following a number of specific approaches:

 A time slice approach whereby expanded sections and very high accumulation rate sites, including non-traditional sedimentary deposits (e.g., drift deposits, fjord and semi-enclosed basin deposits, shelf deposits proximal to river systems, rapidly subsiding coral reefs) from key stratigraphic intervals are targeted. The IMAGES program and subsequent work identified regions in the Indo-Pacific Warm Pool with very high accumulation rates, some in excess of 100 cm kyr^-1, whereas additional natural synergies exist with lake records generated through ICDP (Thurow et al., 2009).

 Use ocean drilling to extend those records that have been demonstrated to be correlateable to high-resolution ice-core records throughout the Quaternary and beyond (Hodell and Abrantes, 2009). Few marine sediment cores have played such a pivotal role in paleoclimate research as those recovered from the Portuguese margin (referred to as the ‗Shackleton sites‘ by Hodell and Abrantes, 2009). These cores preserve a high-fidelity record of millennial–scale climate variability for the last several glacial cycles and can be readily correlated to Greenland ice cores. Alley

(2003) suggested that paleoceanographers should consider following the ice core community‘s lead and organize a research effort to ―generate a few internationally coordinated, multiply replicated, multiparameter, high time resolution-type sections of oceanic change.‖ These types of records were identified by IPCC community members as a crucial component of data-model integration. There is wide interest and support within the paleoceanographic community in seeing the Shackleton sites drilled. At a recent IODP-ICDP workshop (Thurow et al., 2009), the Shackleton sites were identified as a key target for future IODP drilling to obtain marine sediment analogues to the polar ice cores, and this effort resulted in a European Science Foundation funded workshop on drilling the Iberian Margin held in November 2009 in Lisbon, Portugal.

 The IODP consultation in preparation for INVEST (CHART report, 2009) identified the urgent need to conduct the strategic collection of high-resolution data in a geographically distributed fashion, following the GEOSECS approach (‗PALEOSECS‘).

 For several ‗extreme‘ and large amplitude events throughout the Cenozoic, ultrahigh-resolution records are required to fully decipher the complex interplay of climate system components (see sections 5.2.1, 5.2.2, 6.1, 6.2 and 6.3). Of specific interest is the paleo-latitudinal gradient of SST (Bijl et al., 2009; Fig. 2.7)

Figure 2.7 Early and Middle Eocene latitudinal SST gradients compared to modern values. SST gradients during the Eocene are much lower for latitudes south of 60˚S and N than today, and challenge existing climate models (Huber, 2008), from Bijl et al. (2009).

High-resolution and ultrahigh-resolution records can address aspects regarding the causes and consequences of past climate variability, including the nature and origin of abrupt climate change at various timescales, thus providing the opportunity for immediate engagement with the modeling community. The causes of climate variability in the multi-decadal band is currently a key topic in climate prediction and accessible to the high resolution drilling/coring community. Those records are of prime importance to investigate past variability and potential teleconnections of the most important elements of the modern climate system, such as the ENSO, monsoons, the North Atlantic Oscillation, the Pacific Decadal Oscillation, the Arctic Oscillation, and the Southern

Annular Mode under different boundary conditions. High- to ultrahigh-resolution records can also address specific questions such as the timing and magnitude of ice-sheet change, impact of meltwater pulses in the oceans, changes in vertical mixing rates, and the variability of the bipolar seesaw during glacial and interglacial intervals.

High- to ultrahigh-resolution records of sedimentary archives deposited during previous warm intervals (e.g., Early Holocene, Eemian, mid-Pliocene, MMCO, Eocene) over the widest possible geographical range may potentially document the Earth‘s hydrologic, atmospheric, and oceanic responses to past extreme warm events, including the potential occurrence of a seasonal sea-ice cycle, ocean productivity, and ENSO and monsoon variability.