Holocene summer temperature reconstruction from sedimentary chlorophyll content, with treatment of age uncertainties, Kurupa Lake, Arctic Alaska

Brandon R. Boldt, Darrell S Kaufman, Nicholas P. McKay, Jason P. Briner

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

Quantitative records of pre-industrial temperature changes are fundamental for understanding long-term natural climate variability. We used visible reflectance spectroscopy to measure chlorophyll content (and its derivatives) in a sediment core from Kurupa Lake, north-central Brooks Range, Alaska, to reconstruct summer temperature and the number of annual non-freezing days over the past 5.7 ka. A calibration-in-time approach was used to convert downcore changes in chlorophyll content to the climate variables, and an ensemble approach was used to integrate age and calibration uncertainties. The strongest correlation (rmedian = 0.69, pmedian = 0.02, RMSEP = 1.9°C) is for summer (June through September) temperature using the 20th Century Reanalysis Project dataset. The chlorophyll-inferred 3-year-mean summer temperature shows that the warmest century (3.0–2.9 ka BP) was about 3.0°C (90% range of the ensemble members = 2.3–4.0°C) higher and that the coldest century (1.4–1.3 ka BP) was about 5.5°C lower (90% range = −7.6°C to −5.0°C) than during the reference period (AD 1961–1990). Century-to-century temperature changes over the past 5.7 ka at Kurupa Lake have been large (90% range = −2.8°C to 3.1°C shifts in centennial mean), including the shift between the 19th and 20th centuries, which was above the 90th percentile of temperature changes across all representations of the reconstruction. In contrast to most Northern Hemisphere temperature reconstructions, Kurupa Lake shows no overall millennial-scale cooling trend. We suggest that increased summer duration (by 4.3 days during the last 6 ka) along with no long-term increase in sea-ice cover over the adjacent Chukchi Sea counter-balanced the influence of decreased insolation intensity on the aquatic productivity in Kurupa Lake.

Original languageEnglish (US)
Pages (from-to)641-650
Number of pages10
JournalHolocene
Volume25
Issue number4
DOIs
StatePublished - Apr 16 2015

Fingerprint

chlorophyll
Holocene
lake
summer
temperature
calibration
climate
insolation
Uncertainty
Arctic
Temperature
Summer
ice cover
sediment core
sea ice
reflectance
Northern Hemisphere
spectroscopy
cooling
productivity

Keywords

  • age uncertainty
  • Brooks Range
  • Holocene
  • lake sediment
  • paleoclimate
  • proxy-climate record

ASJC Scopus subject areas

  • Archaeology
  • Earth-Surface Processes
  • Global and Planetary Change
  • Ecology
  • Palaeontology

Cite this

Holocene summer temperature reconstruction from sedimentary chlorophyll content, with treatment of age uncertainties, Kurupa Lake, Arctic Alaska. / Boldt, Brandon R.; Kaufman, Darrell S; McKay, Nicholas P.; Briner, Jason P.

In: Holocene, Vol. 25, No. 4, 16.04.2015, p. 641-650.

Research output: Contribution to journalArticle

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AB - Quantitative records of pre-industrial temperature changes are fundamental for understanding long-term natural climate variability. We used visible reflectance spectroscopy to measure chlorophyll content (and its derivatives) in a sediment core from Kurupa Lake, north-central Brooks Range, Alaska, to reconstruct summer temperature and the number of annual non-freezing days over the past 5.7 ka. A calibration-in-time approach was used to convert downcore changes in chlorophyll content to the climate variables, and an ensemble approach was used to integrate age and calibration uncertainties. The strongest correlation (rmedian = 0.69, pmedian = 0.02, RMSEP = 1.9°C) is for summer (June through September) temperature using the 20th Century Reanalysis Project dataset. The chlorophyll-inferred 3-year-mean summer temperature shows that the warmest century (3.0–2.9 ka BP) was about 3.0°C (90% range of the ensemble members = 2.3–4.0°C) higher and that the coldest century (1.4–1.3 ka BP) was about 5.5°C lower (90% range = −7.6°C to −5.0°C) than during the reference period (AD 1961–1990). Century-to-century temperature changes over the past 5.7 ka at Kurupa Lake have been large (90% range = −2.8°C to 3.1°C shifts in centennial mean), including the shift between the 19th and 20th centuries, which was above the 90th percentile of temperature changes across all representations of the reconstruction. In contrast to most Northern Hemisphere temperature reconstructions, Kurupa Lake shows no overall millennial-scale cooling trend. We suggest that increased summer duration (by 4.3 days during the last 6 ka) along with no long-term increase in sea-ice cover over the adjacent Chukchi Sea counter-balanced the influence of decreased insolation intensity on the aquatic productivity in Kurupa Lake.

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