Sensitivity of the biological pump to the Atlantic Meridional Overturning Circulation
Collapse of the Atlantic Meridional Overturning Circulation (AMOC) directly impacts climate in the Atlantic region and indirectly impacts climate on a global basis by altering the ocean's preformed nutrient budget. Modeling results (Schmittner and Lund, 2015) suggest that a weaker AMOC can account for stable isotope and carbonate ion anomalies in the mid-depth Atlantic (Tessin and Lund, 2013; Lund et al., 2015, Lacerra et al., 2017). A weaker AMOC also causes the biological pump to be less efficient on a global basis, which reduces biological export of carbon from the surface ocean and leads to higher atmospheric pCO2, similar to the pattern observed in detailed ice core records. Surface and intermediate depth carbon isotope records from multiple locations are consistent with weakening of the biological pump during both Heinrich Stadial 1 and the Younger Dryas, supporting an AMOC driver of millennial-scale atmospheric CO2 variability during the last deglaciation (Hertzberg et al,. 2016).
Sea level driven variations in mid-ocean ridge magmatism and hydrothermal activity
At mid-ocean ridges, the rate of pressure change from sea level unloading is a substantial fraction of pressure change due to plate spreading, suggesting that sea level may modulate magma flux to ridges on Milankovitch timescales. If hydrothermal activity scales with magma flux, sedimentary hydrothermal proxies can be used to determine if sea-level modulates magmatism at mid-ocean ridges. Further information about this project can be found in Lund & Asimow (2011), Lund et al. (2016) and Lund et al. (2019). Recent work on evidence for anomalous submarine volcanism during the penultimate deglaciation can be found in Lund et al. (2018).
Inferring Holocene variability of the El Niño Southern Oscillation using Borneo stalagmites
ENSO is the primary driver of interannual climate variability today yet little is known about ENSO behavior in the recent past and its overall senstivity to modest climate forcing. Using high-resolution hydroclimate proxies from Borneo, we are attempting to reconstruct ENSO during the Holocene and evaluate whether the frequency and/or magnitude of El Niño events change in response to orbital forcing. Our results thus far suggest the mean climate state of the western equatorial Pacific modulates ENSO variance over the last 10,000 years. A full description of this project can be found in Chen et al. (2016).
Southwest Atlantic watermass evolution during the last deglaciation
Sediment cores from the Brazil Margin are ideally located to monitor the properties of key oceanic watermasses during the last deglaciation, including Antarctic Bottom Water and North Atantic Deep Water. Using stable isotopes, radiocarbon, and trace element analyses, we determined that process in the North Atlantic are most likly responsible for triggering the last deglaciation. Papers with more information on this topic are Sortor and Lund (2011), Tessin and Lund (2013), and Lund et al. (2015). Ongoing work involves evaluating carbon storage in the mid-depth Atlantic on millennial timescales and the implications for atmospheric carbon dioxide (Lacerra et al., 2017). More recently we have focused on carbon loss from the intermediate depth Atlantic during the deglaciation (Lacerra et al., 2019).
Reconstructing the radiocarbon content of the deep Pacific over the past 35,000 years
The deep Pacific is the largest reservoir of readily exchangeable carbon in the ocean-atmosphere system yet little is known about its circulation rate on glacial-interglacial timescales. We are quantifying the ventilation rate of the deep Pacific using high-resolution radiocarbon reconstructions over the last 35 kyr. Our aim is to determine if the Pacific sequestered carbon during the Last Glacial Maximum and then released carbon during the last deglaciation. More informaiton on this project can be found in the following papers: Lund et al. (2011) and Lund (2013).
Stable isotope tracer budget constraints on deep ocean mixing during the Last Glacial Maximum
Qualitative tracers of the ocean circulation are useful for inferring watermass distributions during the Last Glacial Maximum yet little is know about advection and mixing on these time scales. Stable isotope tracer budgets can be used to infer transport to vertical mixing ratios for Antarctic Bottom Water and hence provide insight as to whether the abyssal ocean sequesterd carbon during glaciations. Two papers discussing this topic are Lund et al. (2011) and Hoffman and Lund (2012).
Gulf Stream temperature, salinity and transport during the last millennium
Multiple paleoclimate archives imply that the Little Ice Age was an interval of cooler Northern Hemipshere conditions, particularly in the North Atlantic. A reduction in the Atlantic meridional overturning circulation may have played a role in this cooling, but the lack of quantitative reconstructions of Gulf Stream strength precluded a test of this idea. We estimated Gulf Stream transport for the last millenium and are actively pursuing additional locations where the effects of the wind-driven and overturning components of Gulf Stream flow can be constrained. Relevant papers include Lund and Curry (2004), Lund and Curry (2006), and Lund et al. (2006).