The spatial extent of the Deep Western Boundary Current into the Bounty Trough: new evidence from parasound sub-bottom profiling

Abstract

Deep currents such as the Pacific Deep Western Boundary Current (DWBC) are strengthened periodically in Milankovitch cycles. We studied periodic fluctuations in seismic reflection pattern and reflection amplitude in order to detect cycles in the sedimentary layers of Bounty Trough and bounty fan, east of New Zealand. There, the occurrence of the obliquity frequency is caused only by the DWBC. Therefore, it provides direct evidence for the spatial extent of the DWBC. We can confirm the extent of the DWBC west of the outer sill, previously only inferred via erosional features at the outer sill. Further, our data allow an estimation of the extent of the DWBC into the Bounty Trough, limiting the DWBC presence to east of 178.15°E. Using the presented method a larger dataset will allow a chronological and areal mapping of sedimentation processes and hence provide information on glacial/interglacial cycles.

Data report: clay mineral assemblages within biocalcareous and volcaniclastic inputs to the Hikurangi subduction zone, IODP Expedition 372B/375 Sites U1520 and U1526, offshore New Zealand

“…The DWBC is thought to be the main physical agent responsible for molding the Rekohu contourite drift and sustaining suspensions of sediment in the nepheloid layer (Carter et al, 1996;Carter and Wilkin, 1999). Bounty Channel, which is located far to the south of Site 1124 in the Bounty Trough (Figure F1A), has been responsible for injecting terrigenous clays into the upstream reaches of the DWBC (Hall et al, 2002;; that route for resupplying the DWBC can be tracked farther upstream to terrigenous sources on South Island, New Zealand (Carter and Mitchell, 1987;Carter et al, 1996;Horn and Uenzelmann-Neben, 2016). At times, a vigorous Antarctic Circumpolar Current also may have supplemented supplies of suspended sediment entering upstream parts of the circulation system (Hall et al, 2002).…”