skip to main content

Search for: All records

Creators/Authors contains: "Caffee, Marc W."

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Accurate reconstruction of Laurentide Ice Sheet volume changes following the Last Glacial Maximum is critical for understanding ice sheet contribution to sea-level rise, the resulting influence of meltwater on oceanic circulation, and the spatial and temporal patterns of deglaciation. Here, we provide empirical constraints on Laurentide Ice Sheet thinning during the last deglaciation by measuring in situ cosmogenic 10Be in 81 samples collected along vertical transects of nine mountains in the northeastern United States. In conjunction with 107 exposure age samples over five vertical transects from previous studies, we reconstruct ice sheet thinning history. At peripheral sites (within 200 km of the terminal moraine), we find evidence for ∼600 m of thinning between 19.5 ka and 17.5 ka, which is coincident with the slow initial margin retreat indicated by varve records. At locations >400 km north of the terminal moraine, exposure ages above and below 1200 m a.s.l. exhibit different patterns. Ages above this elevation are variable and older, while lower elevation ages are indistinguishable over 800−1000 m elevation ranges, a pattern that suggests a subglacial thermal boundary at ∼1200 m a.s.l. separating erosive, warm-based ice below and polythermal, minimally erosive ice above. Low-elevation ages from up-ice mountains are betweenmore »15 ka and 13 ka, which suggests rapid thinning of ∼1000 m coincident with Bølling-Allerød warming. These rates of rapid paleo-ice thinning are comparable to those of other vertical exposure age transects around the world and may have been faster than modern basin-wide thinning rates in Antarctica and Greenland, which suggests that the southeastern Laurentide Ice Sheet was highly sensitive to a warming climate.« less
    Free, publicly-accessible full text available December 14, 2023
  2. Free, publicly-accessible full text available November 1, 2023
  3. Abstract. River erosion affects the carbon cycle and thus climate by exporting terrigenous carbon to seafloor sediment and by nourishing CO2-consuming marine life. The Yukon River–Bering Sea system preserves rare source-to-sink records of these processes across profound changes in global climate during the past 5 million years (Ma). Here, we expand the terrestrial erosion record by dating terraces along the Charley River, Alaska, and explore linkages among previously published Yukon Rivertributary incision chronologies and Bering Sea sedimentation. Cosmogenic26Al/10Be isochron burial ages of Charley River terraces match previously documented central Yukon River tributary incision from 2.6 to 1.6 Ma during Pliocene–Pleistocene glacial expansion, and at 1.1 Ma during the 1.2–0.7 Ma Middle Pleistocene climate transition. Bering Sea sediments preserve 2–4-fold rate increases of Yukon River-derived continental detritus, terrestrial and marine organic carbon, and silicate microfossil deposition at 2.6–2.1 and 1.1–0.8 Ma. These tightly coupled records demonstrate elevated terrigenous nutrient and carbon export and concomitant Bering Sea productivity in response to climate-forced Yukon River incision. Carbon burial related to accelerated terrestrial erosion may contribute to CO2 drawdown across the Pliocene–Pleistocene and Middle Pleistocene climate transitions observed in many proxy records worldwide.
  4. Abstract. Sometime during the middle to late Holocene (8.2 ka to ∼ 1850–1900 CE), the Greenland Ice Sheet (GrIS) was smaller than its currentconfiguration. Determining the exact dimensions of the Holocene ice-sheetminimum and the duration that the ice margin rested inboard of its currentposition remains challenging. Contemporary retreat of the GrIS from itshistorical maximum extent in southwestern Greenland is exposing a landscapethat holds clues regarding the configuration and timing of past ice-sheetminima. To quantify the duration of the time the GrIS margin was near itsmodern extent we develop a new technique for Greenland that utilizes in situcosmogenic 10Be–14C–26Al in bedrock samples that have becomeice-free only in the last few decades due to the retreating ice-sheet margin atKangiata Nunaata Sermia (n=12 sites, 36 measurements; KNS), southwest Greenland. To maximizethe utility of this approach, we refine the deglaciation history of the regionwith stand-alone 10Be measurements (n=49) and traditional 14C agesfrom sedimentary deposits contained in proglacial–threshold lakes. We combineour reconstructed ice-margin history in the KNS region with additionalgeologic records from southwestern Greenland and recent model simulations ofGrIS change to constrain the timing of the GrIS minimum in southwestGreenland and the magnitude of Holocene inland GrIS retreat, as well as to explore theregional climate history influencing Holocenemore »ice-sheet behavior. Our10Be–14C–26Al measurements reveal that (1) KNS retreated behindits modern margin just before 10 ka, but it likely stabilized near thepresent GrIS margin for several thousand years before retreating fartherinland, and (2) pre-Holocene 10Be detected in several of our sample sitesis most easily explained by several thousand years of surface exposure duringthe last interglaciation. Moreover, our new results indicate that the minimumextent of the GrIS likely occurred after ∼5 ka, and the GrISmargin may have approached its eventual historical maximum extent as early as∼2 ka. Recent simulations of GrIS change are able to match thegeologic record of ice-sheet change in regions dominated by surface massbalance, but they produce a poorer model–data fit in areas influenced by oceanicand dynamic processes. Simulations that achieve the best model–data fitsuggest that inland retreat of the ice margin driven by early to middleHolocene warmth may have been mitigated by increased precipitation. Triple10Be–14C–26Al measurements in recently deglaciated bedrockprovide a new tool to help decipher the duration of smaller-than-present iceover multiple timescales. Modern retreat of the GrIS margin in southwestGreenland is revealing a bedrock landscape that was also exposed during themigration of the GrIS margin towards its Holocene minimum extent, but it has yetto tap into a landscape that remained ice-covered throughout the entireHolocene.« less