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International Ocean Drilling Program (IODP) Expedition 341 recovered sediments from the south Alaska continental slope that preserves a well resolved and dated inclination record over most of the past ∼43 000 yr. The Site U1419 chronology is among the highest resolution in the world, constrained by 173 radiocarbon dates, providing the ability to study Palaeomagnetic Secular Variation (PSV) on centennial to millennial timescales. This record has an exceptionally expanded late Pleistocene sedimentary record with sedimentation rates commonly exceeding 100 cm kyr–1, while also preserving a lower resolution Holocene PSV record at the top. Natural and laboratory-induced magnetic remanences of U1419 u-channels from the 112-m-long spliced record were studied using stepwise AF demagnetization. Hysteresis loops were obtained on 95 and IRM acquisition curves on 9 discrete samples to facilitate magnetic domain state, coercivity and magnetic mineralogical determinations. Due to complexities related to lithology, magnetic mineralogy, and depositional and post-depositional processes, Site U1419 sediments are not suitable for palaeointensity studies and declination could not be robustly reconstructed. Progressive (titano-)magnetite dissolution with depth results in decreasing NRM intensity and signal-to-noise that is exacerbated at higher demagnetization steps. As a result, inclination measured after the 20 mT AF demagnetization step provides the most reliable directional record.more »Inclination appears to be well resolved with removal of just a few intervals influenced by depositional and/or sampling and coring deformation. The shipboard inclination stack from nearby IODP Site U1418, on a new age model developed from 19 radiocarbon dates on U1418 and 18 magnetic susceptibility-based tie-points to site survey core EW0408-87JC, verifies centennial to millennial scale variations in inclination observed in U1419. Comparisons with other independently dated records from the NE Pacific and western North America suggest that these sites likely capture regional geomagnetic variability. As such, this new high-resolution and well-dated inclination record, especially robust between 15 and 30 cal kyr BP, offers new geomagnetic insights and a regional correlation tool to explore this generally understudied part of the world.

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SUMMARY We present and make publicly available a dynamic programming algorithm to simultaneously align the inclination and declination vector directions of sedimentary palaeomagnetic secular variation data. This algorithm generates a library of possible alignments through the systematic variation of assumptions about the relative accumulation rate and shared temporal overlap of two or more time-series. The palaeomagnetist can then evaluate this library of reproducible and objective alignments using available geological constraints, statistical methods and expert knowledge. We apply the algorithm to align previously (visually) correlated medium to high accumulation rate northern North Atlantic Holocene deposits (101–102 cm ka–1) with strong radiocarbon control. The algorithm generates plausible alignments that largely conform with radiocarbon and magnetic acquisition process uncertainty. These alignments illustrate the strengths and limitations of this numerical approach.

New radiocarbon and sedimentological results from the Gulf of Alaska document recurrent millennial-scale episodes of reorganized Pacific Ocean ventilation synchronous with rapid Cordilleran Ice Sheet discharge, indicating close coupling of ice-ocean dynamics spanning the past 42,000 years. Ventilation of the intermediate-depth North Pacific tracks strength of the Asian monsoon, supporting a role for moisture and heat transport from low latitudes in North Pacific paleoclimate. Changes in carbon-14 age of intermediate waters are in phase with peaks in Cordilleran ice-rafted debris delivery, and both consistently precede ice discharge events from the Laurentide Ice Sheet, known as Heinrich events. This timing precludes an Atlantic trigger for Cordilleran Ice Sheet retreat and instead implicates the Pacific as an early part of a cascade of dynamic climate events with global impact.

Abrupt warming events recorded in Greenland ice cores known as Dansgaard-Oeschger (DO) interstadials are linked to changes in tropical circulation during the last glacial cycle. Corresponding variations in South American summer monsoon (SASM) strength are documented, most commonly, in isotopic records from speleothems, but less is known about how these changes affected precipitation and Andean glacier mass balance. Here we present a sediment record spanning the last ~50 ka from Lake Junín (Peru) in the tropical Andes that has sufficient chronologic precision to document abrupt climatic events on a centennial-millennial time scale. DO events involved the near-complete disappearance of glaciers below 4700 masl in the eastern Andean cordillera and major reductions in the level of Peru’s second largest lake. Our results reveal the magnitude of the hydroclimatic disruptions in the highest reaches of the Amazon Basin that were caused by a weakening of the SASM during abrupt arctic warming. Accentuated warming in the Arctic could lead to significant reductions in the precipitation-evaporation balance of the southern tropical Andes with deleterious effects on this densely populated region of South America.