About

• Summary of Results
• Project Timeline
• Funded Projects
• Borehole Locations
• Site Characteristics
• Replicate Coring, Borehole Logging, Basal Science

Summary of Results

Ice cores are highly valued in paleoclimate research because they record environmental parameters that range on spatial scales from individual snowflakes to the Earth's atmosphere and on time scales from hours to hundreds of millennia. Ice cores are our only source of samples of the paleoatmosphere. They are especially valuable for investigating climate forcing and response, because they record many aspects of the climate system in a common, well-dated archive.

The main objective of the WAIS (West Antarctic Ice Sheet) Divide ice core project (drilling operations from 2006-2013) was to investigate climate from the last glacial period to modern conditions, with greater time resolution than previous Antarctic ice cores. In addition, the project investigated the dynamics of the West Antarctic Ice Sheet and cryobiology. Funding was provided by the United States National Science Foundation (NSF) through the United States Antarctic Program. The distinguishing characteristic of the project was the development of environmental records of the last glacial period and early Holocene, with greater time resolution and dating precision than previous Antarctic ice cores. This is particularly true for the records of atmospheric gases, water isotopes, and chemistry.

Map of West Antarctica. Locations of the WAIS Divide (WDC), Byrd, and Siple Dome ice cores and the Ohio Range (OR) and Mt. Waesche (MW) are shown. Ice shelves are shown in gray. Siple Coast and Amundsen Sea ice streams are shown by blue shading. Contour interval is 500 meters. Credit: T.J. Fudge

A site in Antarctica was required to provide a Southern Hemisphere equivalent to the deep Greenland ice cores. An Antarctic site also allowed development of a more detailed record of atmospheric carbon dioxide, which cannot be obtained in Greenland due to in situ reactions associated with the higher levels of impurities in Greenlandic ice. The selected site was near an ice-flow divide and characterized by a combination of moderate ice accumulation rate, thick ice, and other characteristics that preserved environmental records with the desired time resolution and duration (Morse et al., 2002; Neumann et al., 2008).

Logistics support for field operations was initially provided by Raytheon Polar Services Company and later by NSF's Antarctic Support Contractor. Air transport was provided by the 109th Airlift Wing of the New York Air National Guard. Drilling support was provided by the Ice Drilling Program Office and the Ice Drilling Design and Operations group at the University of Wisconsin, Madison. Drilling was halted 50 meters above the bed at a depth of 3405 meters to leave an environmental barrier between the drilling fluid and the pristine basal aqueous environment. Additional core was collected from five zones of special interest by drilling through the side of the borehole and collecting a total of 285 meters of core nearly parallel to the main core. This major advance in ice coring technology left the entire main hole intact for borehole logging.

The core was sampled at the National Science Foundation - Ice Core Facility (NSF-ICF) — formerly the National Ice Core Laboratory (NICL) — in Denver, Colorado, and subsamples where sent to 17 individually funded institutions for analysis. The Science Coordination Office, at the Desert Research Institute (Nevada System of Higher Education) and University of New Hampshire, coordinated the science, logistics, drilling, and sampling.

The high accuracy of dating was possible due to many factors. A drill site with relatively thick annual layers and other favorable characteristics was selected (Morse et al., 2002). Improvements in drilling (Shturmakov et al., 2007) and core handling (Souney et al., 2014) resulted in exceptional core quality. New core analysis methods with high time resolution were utilized (Ahn et al., 2009; Rhodes et al., 2013, 2015; McConnell et al., 2002, 2007; Fudge et al., 2016b). The WAIS Divide ice core provides a new reference chronology for Antarctica ice cores, enabling detailed reconstructions of paleotemperatures, volcanic forcing, and anthropogenic pollution histories (PAGES 2k Consortium, 2013; Steig et al., 2013; McConnell et al., 2014).

The most recent 31 ka was dated by continuously counting annual layers identified in records of electrical conductivity, multi-parameter aerosols, and trace elements (Sigl et al., 2016; McGwire et al., 2011). Continuous identification of annual layers to this age was a major advance for Antarctic ice cores, enabling synchronization of ice cores from Greenland and Antarctica. This clarified the influence of volcanic eruptions on climate, societal disruptions, famines, and pandemics during the last 2500 years (Sigl et al., 2014, 2015) and demonstrated that cooling from volcanic sulfate aerosols is the primary driver of short-term climate variability (Sigl et al., 2013, 2014, 2015). High-resolution, multi-parameter measurements coupled with exact synchronization between Greenland and Antarctic ice cores underpinned detailed investigation of extreme cosmic ray events during the first millennium (Mekhaldi et al., 2015), as well as evaluation of biomass burning and other aerosols in Earth System Model simulations (Bisiaux et al., 2012; Bauer et al., 2013; Lee et al., 2013; Lamarque et al., 2013).

The annual layer time scale and simple ice flow at the site resulted in the first record of ice accumulation rate during the last deglaciation that is independent of an assumed relationship to water stable isotopes. The ice accumulation rate did not consistently correlate with water isotopes, particularly at times of abrupt climate change in the Northern Hemisphere (Fudge et al., 2016a, 2016b). This calls into question the common practice of using water isotopes as a surrogate for the ice accumulation rate (West Antarctic Ice Sheet (WAIS) Divide Project Members, 2013; Buizert et al., 2015).

The time period from 31 ka to 68 ka was dated using stratigraphic techniques to tie the record to records of other ice cores and radiometrically dated speleothems (Buizert et al., 2015). In ice cores, the age of the ice is older than the age of the atmospheric gases that are trapped in the ice. At WAIS Divide this delta age was a half to a tenth smaller than in most other deep Antarctic cores. The low uncertainty in delta age made it possible to more accurately determine the relative timing of changes in atmospheric carbon dioxide and Antarctic climate during the last deglaciation, conclusively showing the close coupling between the concentration of carbon dioxide in the atmosphere and climate (Marcott et al., 2014).

The high temporal resolution of the atmospheric carbon dioxide record revealed three abrupt increases in carbon dioxide at the times of major climate events (Heinrich Stadial 1, the Bølling warming, and the termination of the Younger Dryas). These enigmatic features of the deglaciation have spurred a discussion of the possible sources of carbon capable of responding to climate on the centennial-scale (Bauska et al., 2016). The high temporal resolution also allowed detailed records of late Holocene variability in the concentration (Ahn et al., 2012) and isotopic composition (Bauska et al., 2015) of atmospheric carbon dioxide, revealing multidecadal changes in land carbon storage.

The detailed atmospheric methane record defined new modes of variability, including sharp increases during some of the cold Greenland "Heinrich" stadials. This led to a hypothesis that extreme southward migration of the Intertropical Convergence Zone during the Greenland stadials activated Southern Hemisphere methane sources (Rhodes et al., 2015). During Heinrich Stadial 1, this possible Southern Hemisphere source of methane is directly associated with an abrupt rise in atmospheric carbon dioxide. Additional work constrained the anthropogenic contribution to atmospheric methane during the late Holocene (Mitchell et al., 2013), possibly including preindustrial human influence (Mischler et al., 2009), and other details of methane during the Holocene period (Sowers, 2010).

The large amounts of high-quality ice facilitated progress in ice core trace gas research. New advancements include measurements of ultratrace level gases such as carbonyl sulfide and ethane that provide new constraints on the global carbon cycle and the atmospheric methane budget (Aydin et al., 2014, 2016; Nicewonger et al., 2015).

The improved dating showed that the abrupt temperature changes in Greenland associated with the Dansgaard-Oeschger events were followed by opposing temperature changes in the Antarctic, ~200 years later. This was observed for both warming and cooling and for larger and smaller events (West Antarctic Ice Sheet (WAIS) Divide Project Members, 2015). This northern lead pattern is consistent with the hypothesis that abrupt reduction of heat transport between the hemispheres by the Atlantic Meridional Overturning Circulation, driven by changes in deep water sinking in the North Atlantic, links the climate of the Northern and Southern Hemispheres during these events (West Antarctic Ice Sheet (WAIS) Divide Project Members, 2015). The deuterium excess record from the same time shows that abrupt latitudinal shifts in the southern westerlies occurred in phase with the Dansgaard-Oeschger events, with no discernable lag (Markle et al., 2017). This clarifies the role of both the ocean and the atmosphere in propagating abrupt climate change between the hemispheres.

The record of paleosurface temperature was determined using a combination of borehole paleothermometry (Orsi et al., 2012), water isotopes (Steig et al., 2013; WAIS Divide Project Members, 2013, 2015; Jones et al., 2016), isotopes of atmospheric nitrogen which are linked to the thickness of the firn (Buizert et al., 2015), bubble characteristics which are linked to processes in the firn (Fegyveresi et al., 2016a, 2016b), and the ice accumulation rate (Fudge et al., 2016a). This integrated approach provided an exceptionally well-constrained record of past surface temperature (Cuffey et al., 2016). The result confirmed that global temperature changes were amplified in the Antarctic and that Antarctica warmed substantially by 15 ka, coincident with glacier retreat in Southern Hemisphere mountain ranges. The combination of ice core and borehole temperature data also provides independent confirmation (Orsi et al., 2012; Steig and Orsi, 2013) of the recent, rapid warming of West Antarctica, previously inferred from the sparse instrumental record (Steig et al., 2009; Bromwich et al., 2013).

The water stable isotope record shows distinct differences from records in central East Antarctica cores. In particular, the West Antarctic isotopic warming began ~2 ka prior to the East Antarctic warming at ~18 ka, indicating an influence of orbital forcing (WAIS Divide Project Members, 2013). Climate model simulations, coupled with measurements of the novel water-isotope parameter ¹⁷O_excess, show that the early warming was amplified by a reduction in sea ice, forced by the local insolation change (Schoenemann et al., 2014).

The physical properties of the core provided a window into deformational processes in the ice sheet as recorded by the layering and characteristics of the c axis and ice grains. The ice flow did not disrupt the climate record, except for centimeter-scale features (Fitzpatrick et al., 2014; Fudge et al., 2016a, 2016b). The numerous crusts in the ice core did not affect the trapped-gas records (Mitchell et al., 2015) because they do not incorporate refrozen meltwater in large volumes (Orsi et al., 2015), and they typically were broken into polygonal patterns by contraction from nighttime cooling in the days after they formed on the surface (Fegyveresi et al., 2016a, 2016b). Snow accumulation rates do impact gas trapping in firn through snow microstructure characteristics (Gregory et al., 2014).

Analysis of the depth-age and temperature profiles with thermomechanical ice-flow models suggests that the ice thickness at WAIS Divide has not changed by more than a few hundred meters during the last 70 ka (Koutnik et al., 2016). The divide is currently migrating toward the Ross Sea at a rate of ~10 m/yr (Conway and Rasmussen, 2009; Koutnik et al., 2016). They hypothesized that the migration is a result of dynamical thinning that is presently stronger in the Amundsen Sea sector than in the Ross Sea sector. The site does not provide information on the status of WAIS during MIS-5e because basal melting would have melted any ice from that time (WAIS Divide Project Members, 2013).

Biology was an integral part of the project. Research on the core showed that prokaryotic cells respond to large-scale environmental and climatic processes on millennial time scales. Higher cell concentration occurred during the Last Glacial Maximum and the early Holocene than during the last deglaciation. Collectively, the data reveal that variability in prokaryotic cell concentration may reflect changes in marine/sea ice regional environments related to sea ice extent, sea level rise, and ice sheet retreat (Santibañez et al., 2016).

In addition to these and many more science results, the project left an archive of ice for future investigations and developed a new generation of ice core researchers who will build on these results for decades to come.

Project Timeline

Table 1. Timeline of major project activities

Field season	Major activities
2005-2006	Establishment of seasonal field camp at WAIS Divide Began construction and assembly of drilling and core handling/processing arch facility Drilled several shallow ice cores
2006-2007	Began interior arch construction activities Drilled 130 meter ice core outside of arch facility Drilled and cased 100 meter pilot hole inside arch facility (0-114m) Installed two DISC Drill gantry cranes inside arch
2007-2008	Finished arch construction Installed DISC Drill Installed core handling/processing equipment Began deep drilling with DISC Drill (114-580 m)
2008-2009	Deep drilling with DISC Drill (brittle ice) (580-1514 m)
2009-2010	Deep drilling with DISC Drill (1514-2564 m)
2010-2011	Deep drilling with DISC Drill (2564-3331 m)
2011-2012	Borehole Logging: Clow (I-475; temperature), Waddington/Anandakrishnan (I-162; sonic), Pettit/Obbard (I-166; televiewer/borehole deformation), and Peters (I-161; seismic) Deep drilling with DISC Drill (3331-3405 m) Replicate Coring Test
2012-2013	Replicate Coring (285 meters of replicate core collected from five deviations)
2013-2014	The partial U.S. government shutdown forced significant changes to the U.S. Antarctic Program's operations for the 2013-2014 field season. The WAIS Divide field camp was not opened and the scientific field operations that were scheduled were postponed to the 2014-2015 field season.
2014-2015	Borehole Logging: Clow (I-475; temperature), Bay/Talghader (I-172; optical), Pettit/Obbard (I-166; televiewer/borehole deformation), and Peters (I-161; seismic) Disassembled and packed DISC Drill at WAIS Divide Disassembled and packed core handling equipment at WAIS Divide Began arch deconstruction (interior facility materials and equipment) Retrograded items based on opportunity of available flights
2015-2016	Secured WAIS Divide borehole to preserve it for any future borehole logging or sampling Finished disassembly and packing of DISC Drill at WAIS Divide Retrograded items based on opportunity of available flights
2016-2017	Borehole Logging: Pettit/Obbard (I-166; televiewer/borehole deformation) Retrograded items based on opportunity of available flights

Table 2. Summary of drilling and core-handling progress for the WAIS Divide deep ice core

Field season	Drill used	Depths drilled (m)	Total depth drilled (m)	Total drilling days	Depths shipped to NICL (m)	Total shipped to NICL (m)
2006-2007	4-Inch	0-114	114	5	0-114	114
2007-2008	DISC	114-580	466	17	114-577	463
2008-2009	DISC	580-1514	934	37	-	0
2009-2010	DISC	1514-2564	1050	45	577-2001	1424
2010-2011	DISC	2564-3331	767	43	2001-3331	1330
2011-2012	DISC	3331-3405	74	7	3331-3405	74

*As anticipated, the brittle ice zone was encountered during the 2008-2009 season. All of the brittle ice was stored in the core storage basement and allowed to winter-over at WAIS Divide to give the ice more time to relax before shipment to the National Science Foundation - Ice Core Facility (NSF-ICF) — formerly the National Ice Core Laboratory (NICL). All of the brittle ice was shipped to the NICL during the 2009-2010 season.

Table 3. Summary of core-processing line (CPL) activities at the National Science Foundation - Ice Core Facility

Austral summer	Depths processed (m)	Total depth processed (m)	Total CPL days	Ave. processing rate (m d-1)	Samples cut
2007	0-114	114	3	38	473
2008	114-577	463	12	39	2857
2009*	-	-	-	-	-
2010	577-1953	1376	51	27	5699
2011	1953-3331	1378	50	28	8552
2012	3331-3405	74	3	25	580

*There was no CPL in 2009 because all of the ice drilled during the 2008-2009 field season was allowed to winter-over at WAIS Divide due to its brittle nature.

Funded Projects

The WAIS Divide ice core was sampled at the National Science Foundation - Ice Core Facility (NSF-ICF) — formerly the National Ice Core Laboratory (NICL) — in Denver, Colorado, and subsamples where sent to 17 individually funded institutions for analysis. Approximately 50 separate but synergistic projects received funding by the National Science Foundation to analyze the ice and interpret its records.

1. A Study of Atmospheric Dust in the WAIS Divide Ice Core Based on Sr-Nd-Pb-He Isotopes: Kaplan M.
2. Acoustic Logging of the WAIS Divide Borehole (Collaborative Research): Waddington E., Anandakrishnan S.
3. Anisotropy, Abrupt Climate Change, and the Deep Ice in West Antarctica (Collaborative Research): Pettit E., Waddington E.
4. Atmospheric Carbon Dioxide and Climate Change: The WAIS Divide Ice Core Record: Brook E.
5. Completing the WAIS Divide Ice Core CO2 record: Brook E.
6. Atmospheric, Snow and Firn Chemistry Studies for Interpretation of WAIS Divide Cores: Frey M. and Bales R.
7. Carbonyl Sulfide Measurements in the Deep West Antarctic Ice Sheet Divide Ice Core: Aydin M. and Saltzman E.
8. Climate, Ice Dynamics and Biology Using a Deep Ice Core from the West Antarctic Ice Sheet Ice Divide (Collaborative Research):Taylor K., Twickler M.
9. Climatology, Meteorology, and Microbial Metabolism in Ice with Dust Loggers and Fluorimetry: Price P.B.
10. Climatology, Volcanism, and Microbial Life in Ice with Downhole Loggers: Price P.B.
11. Collaborative Research: Synchronizing the WAIS Divide and Greenland Ice Cores from 30-65 ka BP Using High-resolution 10Be Measurements: Welten K., Caffee M.
12. Constraining Englacial Temperatures through Active Seismic Methods: Peters L. and Anandakrishnan S.
13. Constructing an Ultra-high Resolution Atmospheric Methane Record for the Last 140,000 Years from WAIS Divide Ice Core (Collaborative Research): Brook E., Sowers T.
14. Completing an Ultra-High Resolution Methane Record from the WAIS Divide Ice Core (Collaborative Research): Brook E., Sowers T.
15. Cosmogenic Radionuclides in the Deep WAIS Divide Core (Collaborative Research): Caffee M., Welten K. and Nishiizumi K.
16. Cosmogenic Radionuclides in the WAIS Divide Ice Core (Collaborative Research): Caffee M., Welten K. and Nishiizumi K.
17. Detection of Crystal Orientation Fabrics near the Ross/Amundsen Sea Ice-flow Divide and at the Siple Dome Ice Core Site using Polarimetric Radar Methods: Raymond C.F. and Matsuoka K.
18. Developing a glacial-interglacial record of delta-13C of atmospheric CO2: Brook E. and Mix A.
19. Establishing the Chronology and Histories of Accumulation and Ice Dynamics for the WAIS Divide Core (Collaborative Research): Waddington E., Taylor K.
20. Firn Metamorphism: Microstructure and Physical Properties: Albert M.
21. Fugitive Gases (Helium, Neon, and Oxygen) in the WAIS Divide Ice Core as Tracers of Basal Processes and Past Biospheric Carbon Storage: Severinghaus J.
22. Gases in Firn Air and Shallow Ice at the Proposed WAIS Divide Drilling Site (Collaborative Research): Sowers T., Brook E., Battle M., White J., Saltzman E. and Aydin M., Severinghaus J.
23. Glaciological Characteristics of the Ross/Amundsen Sea Ice-flow Divide Deduced by a New Analysis of Ice-penetrating Radar Data: Raymond C.F. and Matsuoka K.
24. High Temporal Resolution Black Carbon Record of Southern Hemisphere Biomass Burning: Taylor K.
25. Histories of accumulation, thickness and WAIS Divide location from radar layers using a new inverse approach: Waddington E. and Conway H.
26. Ice Cores, Transluscent Truths from the West Antarctic Ice Sheet: McKee A.
27. Integrated High Resolution Chemical and Biological Measurements on the Deep WAIS Divide Core (Collaborative Research): Priscu J. and Foreman C., Saltzman E., McConnell J. and Edwards P.R.
28. Investigating Source, Chemistry and Climate changes using the Isotopic Composition of Nitrate in Antarctic Snow and Ice: Hastings M.
29. Investigating Upper Pleistocene Rapid Climate Change using Continuous, Ultra-High-Resolution Aerosol and Gas Measurements in the WAIS Divide Ice Core (Collaborative Research): McConnell J., Brook E.
30. Investigation of Climate, Ice Dynamics and Biology using a Deep Ice Core from the West Antarctic Ice Sheet Ice Divide: Taylor K.
31. Investigation of the Stratigraphy and Timescale of the WAIS Divide Ice Core Using Electrical Methods: Taylor K.
32. Major Ion Chemical Analysis of Brittle Ice in the WAIS Divide Ice Core: Cole-Dai J.
33. Major Ion Chemistry of WAIS Divide Ice Core: Cole-Dai J.
34. Measuring an Ice-core Proxy for Relative Oxidant Abundances over Glacial-interglacial and Rapid Climate changes in a West Antarctic Ice Core: Alexander B.
35. Methane Isotope Variations Covering the Holocene from the WAIS Divide Core: Sowers T.
36. Microparticle/tephra analysis of the WAIS Divide ice core (Collaborative Research): Kreutz K., Mayewski P., Wells M. and Kurbatov A., Dunbar N.
37. Multi-parameter Selection Curves for Machine-assisted Annual Layer Interpretations of the WAIS-Divide Core: McGwire K.
38. Multiple-isotope Analysis of Nitrate and Sulfate in the West Antarctic Ice Sheet Divide Ice Core (Collaborative Research): Steig E. and Alexander B., Thiemens M.
39. Nitrogen and Oxygen Gas Isotopes in the WAIS Divide Ice Core as Constraints on Chronology, Temperature, and Accumulation Rate: Severinghaus J.
40. Noble Gases in the WAIS Divide Ice Core as Indicators of Local and Mean-ocean Temperature: Severinghaus J.
41. Optical Fabric and Fiber Logging of Glacial Ice (Collaborative Research): Bay R., Talghader J.
42. Optical Imaging Support for the National Ice Core Laboratory: McGwire K.
43. Paleo Records of Biotic and Abiotic Particles in Polar Ice Cores: Priscu J. and Foreman C.
44. Physical Properties of the WAIS Divide Deep Core (Collaborative Research): Alley R., Voigt D. and Reusch D., Cuffey K.
45. Continued Study of Physical Properties of the WAIS Divide Deep Core (Collaborative Research): Alley R., Spencer M.
46. Preparation for a Deep Ice Coring Project in West Antarctica: Taylor K.
47. Record of the 17O-excess of H2O in the WAIS Ice Core: Steig. E.
48. Replicate Coring at WAIS Divide to Obtain Additional Samples at Events of High Scientific Interest (Collaborative Research): Cole-Dai J., Severinghaus J., Brook E.
49. Self-consistent Ice Dynamics, Accumulation, Delta-age, and Interpolation of Sparse Age Data using an Inverse Approach: Waddington E.
50. Spatial Variability in Firn Properties from Borehole Optical Stratigraphy at the Inland WAIS Core Site: Waddington E.
51. Stable Isotopes of Ice in the Transition and Glacial Sections of the WAIS Divide Deep Ice Core (Collaborative Research): White J., Steig E.
52. Stable Isotopes of Ice in the WAIS Divide Deep Ice Core (Collaborative Research): White J., Steig E., Cuffey K.
53. Tephrochronology of the WAIS Divide Ice Core: Linking Ice Cores through Volcanic Records: Dunbar N.
54. Trace and Ultra-Trace Chemistry Measurements of the WAIS Divide Ice Core: McConnell J.
55. VeLveT Ice - eVoLution of Fabric and Texture in Ice at WAIS Divide, West Antarctica (Collaborative Research): Pettit E., Obbard R.
56. WAIS Divide: Fluorimetry, Dust Logs, Climatology, Glaciology, Volcanology: Price P.B.
57. Western Divide West Antarctic Ice Cores (WAISCORES) Site Selection: Conway H. and Waddington E.

Borehole Locations

Hole	Year(s) Drilled	Drill Used	Core Diameter (mm)	Top Depth (m)	Bottom Depth (m)	Latitude	Longitude	Remarks
WDC12A	~1/13/2012	Eclipse	81	0	121.5	79°27.86' S	112°06.69' W	The top 2 meters of the hole is cased and the casing extends to 2 meters above the current snow surface. An additional 1.5 meters of casing is being stored in the Arch for extension in the future.
WDC06A	2006-2012	DISC	122	114	3405	79.467° S	112.085° W	Deep core. 2006-2007 0-114m. 2007-2008 114-577m. 2008-2009 577-1514m. 2009-2010 1514-2564. 2010-2011 2564-3331. 2011-2012 3331-3405m.
WDC06A	2006	4-Inch	104	0	114	79.467° S	112.085° W	Deep core
WDC06B	2006	4-Inch	104	0	130	79°28.048' S	112°05.160' W
WDC05A	2005	4-Inch	104	0	299	79°28' S	112°05' W	Collected for gas analysis
WDC05B	2005	Eclipse	81	0	75	79°27.775' S	112°07.422' W	Hole drilled for firn gas sampling; core will be used for chemistry method development
WDC05C	2005	Eclipse	81	0	80	79°27.777' S	112°07.362' W	Hole drilled for firn gas sampling; core will be used for chemistry method development
WDC05Q	2005	4-Inch	104	0	130	79°28.052' S	112°05.137' W	Drilled at the arch pit; used for chemistry and isotopes
WDC05E	2005	4-Inch	104	0	32	79°27.777' S	112°07.506' W	Collected for firn structure studies

Site Characteristics

Longitude:	112.085° W
Latitude:	79.467° S
Surface elevation 1:	1,766 m
Distance from current flow divide:	24 km
Current ice-accumulation rate:	22 cm/year
Current average annual surface temperature:	-30°C
Ice thickness:	3,465 m
Ice age-gas age difference in Holocene 2:	200 years
Ice age-gas age difference in the glacial period 2:	500 years

¹ Determined from pole measurements using processed GPS data at the site. Note that this elevation is referenced to WGS84. Source: Conway and Rasmussen, 2009.

² Marcott SA, Bauska TK, Buizert C, Steig EJ, Rosen JL, Cuffey KM, Fudge TJ, Severinghaus JP, Ahn J, Kalk M, McConnell JR, Sowers T, Taylor KC, White JWC and Brook EJ (2014) Centennial-scale changes in the global carbon cycle during the last deglaciation. Nature, 514, 616-619, 10.1038/nature13799

Map of West Antarctica. Locations of the WAIS Divide, Byrd, and Siple Dome ice cores are shown. Siple Coast and Amundsen Sea ice streams are shown by blue shading. Contour interval is 500 meters. Credit: Howard Conway

Replicate Coring, Borehole Logging, Basal Science

The WAIS Divide science and implementation plan, the funded proposal to build the drill, and the funded proposal to conduct field operations, all call for replicate coring to recover additional ice from depth intervals of special interest, borehole logging, and basal sampling of basal water and geologic material.

During the 2007 WAIS Divide science meeting, two groups were formed to investigate: (i) replicate coring and borehole logging, and (ii) basal sampling. The replicate coring and borehole logging group consisted of Ed Brook, Erin Pettit, Jinho Ahn, and Todd Sowers. The basal sampling group consisted of John Priscu, Mark Skidmore, and Slawek Tulacyk. Each group was tasked with developing a science and implementation plan, one for replicate coring and borehole logging, and one for basal sampling. The two science and implementation plans were drafted in 2008, input from the community was solicited, and the two plans were subsequently submitted to the WAIS Divide Executive Committee for review.

During the 2008 WAIS Divide science meeting, the Executive Committee discussed the Replicate Coring and Borehole Logging Science and Implementation Plan and voted to endorse the plan. The plan was subsequently forwarded to NSF and IDPO-IDDO, and Jeff Severinghaus was encouraged to seek funding for the activity. The Executive Committee also discussed the WAIS Divide Basal Science and Implementation Plan, and voted to not endorse the plan at the time. The general concept of the plan had support, but some details needed more attention. The Executive Committee made numerous suggestions to the authors and asked them to resubmit the plan to the Executive Committee.

After reviewing the revised Basal Sampling Science and Implementation Plan, the WAIS Divide Executive Committee, in consultation with the WAIS Divide Community, advised NSF that basal sampling was not a priority for the WAIS Divide project because the basal sampling science objectives would be better met with different drilling methods at different locations by the proposed, and subsequently funded, Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project. As a result, basal sampling at WAIS Divide was pursued no further.

In 2010, Jeff Severinghaus, Jihong Cole-Dai, and Ed Brook submitted a proposal to NSF to conduct replicate coring at WAIS Divide to obtain additional samples at events of high scientific interest, and NSF subsequently funded the proposal. The replicate coring technique, developed and tested by Ice Drilling Design and Operations (IDDO) as part of the Deep Ice Sheet Coring (DISC) drill, is a key advance, because it allows scientists to take samples from specific levels of a parent borehole without impeding the hole itself, leaving the parent borehole open for future logging of information. After testing the replicate coring system at the end of the 2011-2012 field season, the system was deployed in December 2012 to re-enter the deep borehole, and successfully allowed the researchers to drill through the wall of the 3405-meter deep parent hole and collect a total of 285 meters of additional core from five of the most interesting time periods in the WAIS Divide climate record.

Deviation #	Coring Start Depth (m)	Full Diameter By (m)	Coring End Depth (m)
1	3001.55	3006.16	3100.26
2	2416.70	2420.02	2469.49
3	2221.00	2226.16	2290.80
4	1952.00	1956.90	2000.20
5	2414.50	2420.02	2428.74

Table - Replicate Coring. Summary of the five replicate coring deviations carried-out during the 2012-2013 field season. Deviation #1 corresponds to AIM8 and the Laschamp Event. Deviation #2 corresponds to the 18 ka event. Deviation #3 corresponds to the Bølling-Allerød event. Deviation #4 corresponds to the Younger Dryas event. Deviation #5 corresponds (again) to the 18 ka event.

Logging of the WAIS Divide deep borehole was conducted during the 2011-2012 (temperature, sonic, optical, and seismic logging), 2014-2015 (temperature, optical, televiewer/borehole deformation, and seismic logging), and 2016-2017 (televiewer/borehole deformation) field seasons.