Saw-tooth pattern of North Atlantic current speed during Dansgaard-Oeschger cycles revealed by the magnetic grain size of Reykjanes Ridge sediments at 59 degrees N

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T1 - Saw-tooth pattern of North Atlantic current speed during Dansgaard-Oeschger cycles revealed by the magnetic grain size of Reykjanes Ridge sediments at 59 degrees N

AU - Snowball, Ian

AU - Moros, M

PY - 2003

Y1 - 2003

N2 - Detailed mineral (rock) magnetic measurements, including high-resolution magnetic hysteresis loops, were carried out on three sediment cores recovered from the Reykjanes Ridge in the North Atlantic. Supported by physical grain-size analyses, titanomagnetite grain-size variations form a proxy of the speed of near-bottom currents and reveal a cyclic ""saw-tooth'' pattern between Dansgaard-Oeschger cycles 8 and 5. The magnetic grain-size data suggest that these Dansgaard-Oeschger cycles were characterized by gradual intensification of the near-bottom current speed, while other paleoceanographic proxies indicate escalating iceberg discharge and declining sea surface temperatures. These observations are contrary to the frequently assumed and strictly applied positive relationship between high-latitude warmth and North Atlantic Deep Water formation. Within the confines of temporal control, however, it would appear that peaks in iceberg discharge and slow near-bottom current speeds were synchronous. The magnetic hysteresis data also demonstrate that magnetic concentration parameters, such as magnetic susceptibility, do not necessarily provide direct evidence of paleocirculation.

AB - Detailed mineral (rock) magnetic measurements, including high-resolution magnetic hysteresis loops, were carried out on three sediment cores recovered from the Reykjanes Ridge in the North Atlantic. Supported by physical grain-size analyses, titanomagnetite grain-size variations form a proxy of the speed of near-bottom currents and reveal a cyclic ""saw-tooth'' pattern between Dansgaard-Oeschger cycles 8 and 5. The magnetic grain-size data suggest that these Dansgaard-Oeschger cycles were characterized by gradual intensification of the near-bottom current speed, while other paleoceanographic proxies indicate escalating iceberg discharge and declining sea surface temperatures. These observations are contrary to the frequently assumed and strictly applied positive relationship between high-latitude warmth and North Atlantic Deep Water formation. Within the confines of temporal control, however, it would appear that peaks in iceberg discharge and slow near-bottom current speeds were synchronous. The magnetic hysteresis data also demonstrate that magnetic concentration parameters, such as magnetic susceptibility, do not necessarily provide direct evidence of paleocirculation.

KW - circulation

KW - thermohaline

KW - current speed

KW - North Atlantic

KW - magnetic grain-size

KW - Dansgaard-Oeschger cycles

U2 - 10.1029/2001PA000732

DO - 10.1029/2001PA000732

M3 - Article

VL - 18

JO - Paleoceanography

JF - Paleoceanography

SN - 0883-8305

IS - 2

ER -