Deciphering Florida Current History from Paleocurrent Features in the Florida CSL Straits: Insights into North Atlantic Circulation and Global Climate Change
KELLY BERGMAN1 AND GREGOR EBERLI1 1Rosenstiel School of Marine and Atmospheric Science, 4600 Rickenbacker Causeway, Miami, FL, 33149 The Gulf Stream Seismic Facies - Identifying Current Deposition and Erosion
Florida Current history of the past 25 m.y. as revealed by paleocurrent deposits and erosional features in the Florida Straits brings new insight into the timing of Cenozoic circulation change caused by the complex interactions between circulation and global climate change. The modern Florida Current along with the Antilles Current forms the Gulf Stream north of Sediment drifts contain continuous low- Erosional features in the Florida Straights Sand waves are composed of wavy the Bahamas. The Gulf Stream is a amplitude seismic reflections that include erosional channels and discontinuous reflections that indicate western boundary current that generally diverge towards the drift axis. downcutting followed by subsequent fill. traction flow by bottom currents. composes the northward flowing They form elongated mounds parallel to surface limb of the North Atlantic the main axis of current flow within the circulation "conveyor" and is partly channel or along a platform edge. responsible for feeding North Atlantic Deep Water (NADW). NADW is a dense deep-water current that forms in the Labrador and Norwegian Seas and then Line 63 - Santaren Channel Cross-section sinks and flows southward to compose the deep flowing limb of the North Atlantic twtt (s) twtt (s) conveyor. 0.0 0.0 The paleo-Florida Current was first established in the Paleocene and since has been 0.2 0.2 influenced by upstream tectonic changes including closing of the Suwannee Straits 0.4 0.4 and the Central American Seaway. 0.6 0.6 If Gulf Stream waters are critical for NADW formation and NADW is an effective 0.8 0.8 indicator of circulation change, then the current history of the Florida Current would 1.0 1.0 help establish the direct or indirect feedback mechanism between circulation and 1.2 1.2 climate change and the link between climate and tectonic events in the Caribbean. 1.4 1.4 1.6 1.6 1.8 1.8
2.0 2.0 The Straits of Florida 2.2 2.2
0.4 0.4
Throughout the Neogene, the 0.6 0.6 FLORIDA 0 100 km ancestral Florida Current has left 0.8 0.8 E 1.0 3.6 Ma 1.0 behind depositional and 26¡
Miami 1.2 Santaren Drift 1.2 N F erosional current features in the BAHAMAS 5.4 H 9.4 1.4 1.4 K 12.2 Florida Straits through which it M N 15.1 1.6 1.6 P 15.9 19.2 passes on its way to the Atlantic. P2 22.5 Q 23.7 L 1.8 i 1.8 Erosion Precise dating of paleocurrent n Western Line Sand waves e Andros 5 2.0 2.0 3 features was possible by UNDA & Island correlating dates from ODP Leg CLINO 3 166 into a data set of several 24¡ e 6 Lin thousand km's of multi-channel Seismic line 63 with sequence boundaries and interpretations. Continuous seismic reflections 12.2 Ma (upper Middle Miocene, sequence boundary K) drift sedimentation begins in the axis of the seismic lines that cover the prior to 15.9 Ma (sequence boundary N) indicate non-drift basinal sedimentation in the Santaren Santaren Channel and is bounded by sand waves to the east and slump to the west. By 10.7 Ma Great Bahama Florida Straits, a deep narrow Bank Channel. To the southwest towards Cay Sal Bank, reflections increase in transparency and (sequence boudary I), sand waves are absent to rare. Drift sedimentation processes are channel through which the amplitude and contain sporadic slump. Beginning around 15.9 Ma (Middle Miocene), sand waves widespread across the channel by 9.4 Ma (Late Miocene, sequence boudary H). Beginning at 5.4 Florida Current is funneled. CUBA become more widespread and increase in amplitude. Sand waves are concentrated on the Ma (sequency boudary F), reflections within the drift begin to dip to the northeast and downlap 80¡ 78¡ 76¡ northeast side of the channel while slumping occurs on the southwest side. The absence of sand onto slope deposits. Accumulation rates within the Santaren Drift reach up to 370 mm/kyr. At waves on the southwestern side of the channel may be due to slumping that reaches nearly to the around 3.6 Ma (sequence boudary E), the high drift accumulation rates decrease, drift width across center of the channel. Alternatively, bottom currents may have only developed traction flow on the the channel narrows and slope sedimentation dominates the northeast side of the channel. northeast side of the channel.