Paleonutrient and productivity records from the subarctic North Pacific for Pleistocene glacial terminations I to V

Abstract

[1] Our study addresses fundamental questions of the mode and timing of orbital and millennial-scale changes in the meridional overturning circulation (MOC) of the subarctic North Pacific. Particular concerns are the vertical mixing, the present and past abundance of nutrients in surface waters despite strong stratification, and the North Pacific-North Atlantic seesaw of oscillations in sea surface temperature (SST). We do this by generating and interpreting multiple records for glacial terminations I-V down two long piston cores, one each from the western and eastern subarctic Pacific. Chlorins and biogenic opal are proxies for surface water productivity; d 13 C of epibenthic foraminifera is a record of deepwater ventilation; and the d 13 C of N. pachyderma sin. is a tracer of nutrients in subsurface waters that extend up to the sea surface during times of vertical mixing. The degree of mixing is traced by pairing SST and d 18 O records of planktic surface and subsurface (pycnocline) dwellers. Tight age control is deduced from a suite of age-calibrated 14 C plateau boundaries for Termination I and benthic d 18 O and geomagnetic events for the last 800 ka. Carbon 14 paleoreservoir ages record the ages of surface and deep waters to uncover short-term changes in MOC over Termination I. We have defined a standard sequence of short-term productivity events for Termination I, also evident during terminations II to V and subsequent interglacials over the last 450 ka. The peak glacial regime of stable stratification and low productivity terminated, together with the end of ice rafting and melting, near 17 ka, $2000 years after the onset of Termination I. Pulses of vertical mixing and incursion of warm surface waters from the subtropics followed. Convected young water masses finally penetrated down to 3600-m water depth at 17.0 to less than 14.5 ka, significantly improving bottom water ventilation through the late deglacial and earliest interglacial. Mixing with upwelled nutrients from the pycnocline induced short-term maxima in algal production of chlorins and biogenic opal near 17-15 and 15-12 ka, respectively. Deglacial meltwater incursions in the Aleutian Current and silica input from North American rivers also promoted East Pacific productivity after 15.5 ka. Productivity decreased during the late deglacial and early interglacial, coeval with an exceptional peak in CaCO 3 preservation caused by both low organic flux and well-ventilated deepwater. Subsequently, low salinity and cool surface waters and in turn, stratification were gradually restored. A second, opaldominated productivity maximum marked the ends of interglacials. The deglacial pulses of vertical mixing around 17-11 ka imply an important contribution of the North Pacific to the coeval release of oceanic CO 2 into the atmosphere and support the east-west seesaw model of climate change.Citation: Gebhardt, H., M. Sarnthein, P. M. Grootes, T. Kiefer, H. Kuehn, F. Schmieder, and U. Röhl (2008), Paleonutrient and productivity records from the subarctic North ...

Planktic and Benthic14C Reservoir Ages for Three Ocean Basins, Calibrated by a Suite of14C Plateaus in the Glacial-to-Deglacial Suigetsu Atmospheric14C Record

“…As compared to previously published 14 C data of cores GIK17940, MD01-2378, MD01-2416, MD02-2489, ODP893A, and PS2644 (Sarnthein et al 2007Gebhardt et al 2008), the sampling density and reach of 14 C records was increased and the tuning of plateaus carefully reconsidered on the basis of the new atmospheric 14 C reference record of Lake Suigetsu (Bronk Ramsey et al 2012 If one takes an ample uncertainty of 250 14 C yr, incorporating sampling effects and timescale uncertainty, the data in the Suigetsu 14 C age-age plot (Figure 2a) can be seen as scattering around a straight line, which reflects a 14 C timescale that indeed corresponds to real time. However, if one tries to extract more and new information from the record, one zooms in and tries to understand the fine structure of the record and the information it contains, that is, to find all 14 C plateaus and 14 C jumps in between.…”

“…The planktic 14 C record of Core MD02-2489 ( Figure 11; Table S2i) consists of 28 14 C dates measured on N. pachyderma (s) (Gebhardt et al 2008) that constitute an undisturbed record of 14 C, confirmed by 1st derivatives and correlated with Suigetsu plateaus 1-4. They imply sedimentation rates of 23 to ~32 cm/kyr for the LGM and HS-1 as compared to >42 cm/kyr for the B/A, trends that are similar to those at Site MD01-2416.…”

“…This article presents 11 records of glacial-to-early-deglacial planktic and 8 records of benthic 14 C reservoir ages (23-13 cal ka) from the Atlantic, Indian, and North Pacific oceans (Figure 1). Four planktic records are new (GIK 23074, MD08-3180, ODP 1002, andMD02-2503) and four have been augmented with new planktic 14 C dates [(PS2644, GIK17940, and MD01-2416(Sarnthein et al 2007); MD02-2489 (Gebhardt et al 2008)]. Absolute ages and 14 C reservoir ages for the records are derived using the Suigetsu atmospheric 14 C record on its varve-counted timescale instead of the earlier atmospheric proxy 14 C record based on corals, Cariaco planktic forams, and Bahama speleothems.…”

Eolian dust input to the Subarctic North Pacific

“…The 26 stations considered for the dust fraction and flux estimations are indicated in bold. LSRs are assumed based on either paleomagnetic data (Opdyke and Foster, 1970; Lucia Korff, University of Bremen, personal communication) or estimates from downcore studies in the northwest (Keigwin et al, 1992) and northeast SNP (Gebhardt et al, 2008) …”

“…The incomplete consumption has been explained by a lack of dissolved iron for which eolian dust is suggested to be the primary source in the SNP (e.g., Bishop et al, 2002;Duce and Tindale, 1991;Martin and Fitzwater, 1988;Martin et al, 1989; (Natland, 1993) and 881-882 (Cao et al, 1995a). ODP site 887 (Cao et al, 1995b) and MD02-2489 (Gebhardt et al, 2008) are located near stations 26-28, RAMA 44PC (Keigwin et al, 1992) is located near station 5 and the site of core RC10-196 (Kohfeld and Chase, 2011) is located near station 13. The map was created using Ocean Data View 4.3.10 (Schlitzer, 2011).…”