Numerically, values are equivalent to parts salt per thousand parts water.) (The dimensionless unit ‘psu' is used in this article to indicate salinities measured on the Practical Salinity Scale (Lewis 1980). Properties of this inflow vary significantly seasonally, from about 0.4Sv, -1.9✬, and 33psu in winter to about 1.2Sv, greater than 2 ✬, and less than 31.9psu in summer (Woodgate et al. The only Pacific-Arctic gateway is the narrow (~ 85km wide), shallow (~ 50m deep) Bering Strait, through which about 0.8Sv (1Sv=10 6m 3/s) of water enters the Arctic. Its northward migrating crest is interpreted to represent still ongoing current variations of NADW and AABW.The Arctic Ocean plays two roles in the global ocean circulation - it provides an oceanic pathway between the Pacific and the Atlantic oceans and it also takes an Atlantic input, modifies it, and returns it to the Atlantic (Rudels and Friedrich 2000). The overlying Agulhas Drift consists of an asymmetrical body, thickening to the north and the west. Most probably we assume, this drift has been built up by a then N-S flowing branch of the AABW, roughly 15 17 Ma ago. Corresponding to its shape and position, it must have been deposited by currents flowing in a more north-southerly direction, perpendicular to recent flow paths of NADW and AABW, which move in W-E direction. During our investigations we found another quite large drift body located underneath the Agulhas Drift. Later stages are separated by discordances, which represent the onset of AABW and NADW, among others, triggered by the opening of the Drake Passage gateway (~35 Ma ago) and the closure of the Panama Isthmus (~3 Ma ago). The first stage represents ongoing deep sea sedimentation in Middle Cretaceous times. In total, there are at least 4 major sedimentary phases to observe, which seem to be mainly triggered by the influence of NADW and AABW. The analysis of the data showed the effect of large scale current depositions. To map the exact location and dimensions of the Agulhas Drift we gathered about 2800 km of high resolution reflection seismic data in 2005. Here, the northern hemisphere originating NADW and the southern hemisphere originating AABW meet and built up this drift body. South of South Africa in the Transkei Basin the giant elongated Agulhas Drift is located, which, including underlying sediments, is a unique feature for ocean current reconstruction over the past 30 Myrs.
#Circulated water drift archive#
One way to reconstruct these palaeocurrents is a seismostratigraphic analysis of sedimentary structures because they comprise an archive of transport and deposition by ocean currents. Knowing the former current paths improves the knowledge on former climate conditions. Especially thermohaline circulation with water masses like the Antarctic Bottom Water (AABW) or the North Atlantic Deep Water (NADW), are a motor for maintaining the exchange of warm and cold water masses. The Earth`s climate is controlled by many different factors with large scale ocean currents playing a significant role.
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