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5 Marine, Lake, and Cave Proxies
Pages 53-64

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From page 53...
... · Corals and marine sediments provide information about surface temperature in otherwise undersampled ocean regions. Peat and lake muds, which contain microfossils of climate-sensitive organisms, and cave calcite deposits provide information on climate events impacting land areas.
From page 54...
... The 18O of water is often strongly correlated with salinity. Hence, 18 O values from a coral that grew in an open-ocean location can be used to reconstruct a combined signal of sea surface temperature (SST)
From page 55...
... . Other coral records from the southwestern Pacific (Figure 5-2)
From page 56...
... 56 SURFACE TEMPERATURE RECONSTRUCTIONS FOR THE LAST 2,000 YEARS FIGURE 5-2 (A­F) Comparison of interdecadal variability in geochemical records from Porites corals from Rarotonga (Linsley et al.
From page 57...
... 2000) demonstrate an SST increase of 0.6°C from the mid-1800s to 1980; discontinuous records from Madagascar indicate cool conditions from 1675 to 1760 and warm conditions from 1880 to 1900 and from 1973 to 1995 (Zinke et al.
From page 58...
... MARINE SEDIMENTS The utility of marine sediments in recording climate change during the Holocene depends either on sufficiently rapid sediment accumulation to overcome the mixing effects of bioturbation2 (usually up to 8 centimeters) or deposition under anoxic or suboxic oceanic conditions to retain annual layers.
From page 59...
... 1999) and zones of layered sediment deposited under anoxic conditions -- such as fjords along the coast of British Columbia, Canada -- also possess marine sediments with distinct seasonal layers that offer high-resolution histories of late Holocene climate.
From page 60...
... (2003) used Mg/Ca paleothermometry on microfossil shells to show temperature shifts of 2­ 4°C in the Chesapeake Bay, including cold excursions during the Little Ice Age and warmer periods during medieval times (about A.D.
From page 61...
... Although the East Mediterranean was relatively dry during the Little Ice Age, low lake levels in East Africa and North America indicate that droughts in these regions were more extreme in medieval times than during the 20th century, possibly linked to changes in solar activity (Hodell et al. 2001, Verschuren et al.
From page 62...
... millennia, partly because the vegetation that produces pollen lags in its response to climatic forcing. The calibration approach used for all of these organisms is based on modern training sets rather than matching them against past temperature changes in the instrumental record.
From page 63...
... In some cool and wet regions, the cave temperature signal may be dominant in controlling the 18O and other measurements, and this is especially valuable because cave temperature is stable throughout the year and represents the mean annual temperature of the outside environment. Modern speleothem properties have been used to calibrate cave sequences from northern Scandinavia in terms of Holocene temperature variability (Lauritzen and Lundberg 1999)
From page 64...
... . A major challenge in these cases is to ensure that records are accurately dated and correlated because, if they are not, composite records will tend to smooth out the true temperature variability.


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