The sensitivity of southeast pacific heat distribution to local and remote changes in ocean properties

AbstractThe Southern Ocean features ventilation pathways that transport surface waters into the subsurface thermocline on time scales from decades to centuries, sequestering anomalies of heat and carbon away from the atmosphere and thereby regulating the rate of surface warming. Despite its importance for climate sensitivity, the factors that control the distribution of heat along these pathways are not well understood. In this study, we use an observationally constrained, physically consistent global ocean model to examine the sensitivity of heat distribution in the recently ventilated subsurface Pacific (RVP) sector of the Southern Ocean to changes in ocean temperature and salinity. First, we define the RVP using numerical passive tracer release experiments that highlight the ventilation pathways. Next, we use an ensemble of adjoint sensitivity experiments to quantify the sensitivity of the RVP heat content to changes in ocean temperature and salinity. In terms of sensitivities to surface ocean properties, we find that RVP heat content is most sensitive to anomalies along the Antarctic Circumpolar Current (ACC), upstream of the subduction hotspots. In terms of sensitivities to subsurface ocean properties, we find that RVP heat content is most sensitive to basin-scale changes in the subtropical Pacific Ocean, around the same latitudes as the RVP. Despite the localized nature of mode water subduction hotspots, changes in basin-scale density gradients are an important controlling factor on heat distribution in the southeast Pacific.</jats:p

Global Tipping Points 2023 Report: Ch1.4 – Tipping points in ocean and atmosphere circulations.

This chapter assesses scientific evidence for tipping points across circulations in the ocean and atmosphere. The warming of oceans, modified wind patterns and increasing freshwater influx from melting ice hold the potential to disrupt established circulation patterns. We find evidence for tipping points in the Atlantic Meridional Overturning Circulation (AMOC), the North Atlantic Subpolar Gyre (SPG), and the Antarctic Overturning Circulation, which may collapse under warmer and ‘fresher’ (i.e. less salty) conditions. A slowdown or collapse of these oceanic circulations would have far-reaching consequences for the rest of the climate system, such as shifts in the monsoons. There is evidence that this has happened in the past, having led to vastly different states of the Sahara following abrupt changes in the West African monsoon, which we also classify as a tipping system. Evidence about tipping of the monsoons over South America and Asia is limited, however large-scale deforestation or air pollution are considered as potential sources of destabilisation. Although theoretically possible, there is little indication for tipping points in tropical clouds or mid-latitude atmospheric circulations. Similarly, tipping towards a more extreme or persistent El Niño Southern Oscillation (ENSO) state is not sufficiently supported by models and observations. While the thresholds for many of these systems are uncertain, tipping could be devastating for many millions of people. Stabilising climate (along with minimising other pressures, like aerosol pollution and ecosystem degradation) is critical for reducing the likelihood of reaching tipping points in the ocean-atmosphere system

A second generation human haplotype map of over 3.1 million SNPs

We describe the Phase II HapMap, which characterizes over 3.1 million human single nucleotide polymorphisms (SNPs) genotyped in 270 individuals from four geographically diverse populations and includes 25-35% of common SNP variation in the populations surveyed. The map is estimated to capture untyped common variation with an average maximum r(2) of between 0.9 and 0.96 depending on population. We demonstrate that the current generation of commercial genome-wide genotyping products captures common Phase II SNPs with an average maximum r(2) of up to 0.8 in African and up to 0.95 in non-African populations, and that potential gains in power in association studies can be obtained through imputation. These data also reveal novel aspects of the structure of linkage disequilibrium. We show that 10-30% of pairs of individuals within a population share at least one region of extended genetic identity arising from recent ancestry and that up to 1% of all common variants are untaggable, primarily because they lie within recombination hotspots. We show that recombination rates vary systematically around genes and between genes of different function. Finally, we demonstrate increased differentiation at non-synonymous, compared to synonymous, SNPs, resulting from systematic differences in the strength or efficacy of natural selection between populations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62863/1/nature06258.pd

The Role of Ocean Dynamics in King Penguin Range Estimation

In a recent Article, Cristofari et al.1 discuss the impact that movements of the Antarctic Polar Front have had on historical king penguin populations, and make future projections based on potential climate change scenarios. They predict that 70% of the world’s breeding population will be severely impacted as the Polar Front, with its nutrient-rich upwelling and high productivity, moves polewards beyond the foraging range of many penguin colonies. We highlight here, however, that a detailed analysis of the models used does not support the projection of a poleward shift in the Polar Front’s future position, and that recent analyses show no evidence for such a shift having occurred in the last several decades

Zonally asymmetric response of the Southern Ocean mixed-layer depth to the Southern Annular Mode

International audienc

Eddy-induced variability in Southern Ocean abyssal mixing on climatic timescales

PublishedJournal ArticleThis is the author accepted manuscript. The final version is available from Nature Publishing Group via the DOI in this record.The Southern Ocean plays a pivotal role in the global ocean circulation and climate. There, the deep water masses of the world ocean upwell to the surface and subsequently sink to intermediate and abyssal depths, forming two overturning cells that exchange substantial quantities of heat and carbon with the atmosphere. The sensitivity of the upper cell to climatic changes in forcing is relatively well established. However, little is known about how the lower cell responds, and in particular whether small-scale mixing in the abyssal Southern Ocean, an important controlling process of the lower cell, is influenced by atmospheric forcing. Here, we present observational evidence that relates changes in abyssal mixing to oceanic eddy variability on timescales of months to decades. Observational estimates of mixing rates, obtained along a repeat hydrographic transect across Drake Passage, are shown to be dependent on local oceanic eddy energy, derived from moored current meter and altimetric measurements. As the intensity of the regional eddy field is regulated by the Southern Hemisphere westerly winds, our findings suggest that Southern Ocean abyssal mixing and overturning are sensitive to climatic perturbations in wind forcing. © 2014 Macmillan Publishers Limited.The DIMES experiment is supported by the Natural Environment Research Council (NERC) of the UK and the US National Science Foundation. K.L.S. is supported by NERC. We are grateful to J. Ledwell, A. Bogdanoff, P. Courtois, K. Decoteau, D. Evans and X. Liang for their help in data collection and acknowledge the valuable assistance and hard work of the crew and technicians on the RRS James Cook, the RRS James Clark Ross and the RV Thomas G. Thompson. We also thank A. Thompson who provided many helpful comments, and E. Murowinski, R. Lueck and F. Wolk from Rockland Scientific for their support in microstructure data analysis