Mathematics – Logic
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja.....1245g&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #1245
Mathematics
Logic
Scientific paper
Analyses of long European tide-gauge records (Brest, Amsterdam, Stockholm, Swinoujscie, Liverpool) suggest that sea-level rise has accelerated in the 20th century compared to the 19th century. However, similar analyses along western Atlantic coastlines are difficult because instrumental records are too short. We obtained a new high-resolution relative sea-level record based on foraminiferal and chronological analyses of a salt-marsh peat sequence from Chezzetcook on the Atlantic coast of Nova Scotia, containing 20 sea-level data points between 1700 and 1900. The 20th century sea-level change is reconstructed from another 30 sea-level data points and corresponds very well with the tide-gauge measurements at Halifax. The calculated error on former mean tide-level positions is ±7 cm. The peat sequence is dated by 210Pb, 137Cs, AMS14C, 206Pb/207Pb and pollen. The relative sea-level record for the Atlantic coast of Nova Scotia shows a 10 cm rise between 1700 and 1720 followed by a slow and steady rise of 20 cm between 1720 and 1900. In the past 100 years, sea level at Chezzetcook has risen by about 40 cm. We compared the sea-level record from Chezzetcook with two Gulf of Maine records (Wells and Machiasport; Gehrels et al., 2002, The Holocene 12, 383-398). Because isostatic movements are variable in the region we detrended the relative sea-level records based on 1930-2000 tide-gauge trends. A sharp rise in sea level around 1700 shows up in all three detrended records. This rise corresponds with higher Northern Hemisphere temperatures and is therefore interpreted to be glacio-eustatic in origin. However, in the second half of the 18th century sea level fell in the Gulf of Maine while it remained stable in Chezzetcook. Since about 1800 sea levels have steadily risen in the Gulf of Maine, but in Chezzetcook the ongoing sea-level rise started only around 1900. We interpret the differences between the sea-level histories of the Gulf of Maine and Chezzetcook as resulting from oceanographic factors. The Maine Coastal Current in the Gulf of Maine is influenced by freshwater runoff from rivers entering the Gulf of Maine. Land temperatures in eastern North America started to rise around 1800, as shown by ground heat-flux borehole records, and the Gulf of Maine waters may have responded sterically. Palaeoceanographic evidence from cores just south of Newfoundland suggests that surface waters in the North Atlantic Ocean north of the Gulf Stream were cold during medieval times but warmed during the 16th to 19th centuries. Therefore, the sea-level record of Chezzetcook during this time may also reflect, in part, thermal expansion of the surface waters influenced by the Labrador Current. Our results suggest that, during the past millennium, steric change has been an important contributor to sea-level variability in the western Atlantic on decadal to centennial timescales. Rates of 20th century sea-level rise in the western Atlantic are unprecedented in the past millennium.
Black Samson
Gehrels R.
Kirby Jonathan
Newnham R.
Truscott J.
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