Carbon and climate system coupling on timescales from the Precambrian to the Anthropocene

Author Posting. © Annual Reviews, 2007. This is the author's version of the work. It is posted here by permission of Annual Reviews for personal use, not for redistribution. The definitive version was published in Annual Review of Environment and Resources 32 (2007): 31-66, doi:10.1146/annurev.energy.32.041706.124700.The global carbon and climate systems are closely intertwined, with biogeochemical processes responding to and driving climate variations. Over a range of geological and historical time-scales, warmer climate conditions are associated with higher atmospheric levels of CO2, an important climate-modulating greenhouse gas. The atmospheric CO2-temperature relationship reflects two dynamics, the planet’s climate sensitivity to a perturbation in atmospheric CO2 and the stability of non-atmospheric carbon reservoirs to evolving climate. Both exhibit non-linear behavior, and coupled carbon-climate interactions have the potential to introduce both stabilizing and destabilizing feedback loops into the Earth System. Here we bring together evidence from a wide range of geological, observational, experimental and modeling studies on the dominant interactions between the carbon cycle and climate. The review is organized by time-scale, spanning interannual to centennial climate variability, Holocene millennial variations and Pleistocene glacial-interglacial cycles, and million year and longer variations over the Precambrian and Phanerozoic. Our focus is on characterizing and, where possible quantifying, the emergent behavior internal to the coupled carbon-climate system as well as the responses of the system to external forcing from tectonics, orbital dynamics, catastrophic events, and anthropogenic fossil fuel emissions. While there are many unresolved uncertainties and complexity in the carbon cycle, one emergent property is clear across time scales: while CO2 can increase in the atmosphere quickly, returning to lower levels through natural processes is much slower, so the consequences of the human perturbation will far outlive the emissions that caused them.S. Doney acknowledges support from the NSF Geosciences Carbon and Water program (NSF ATM-0628582) and the WHOI W. Van Alan Clark Sr. Chair. D. Schimel acknowledges support from the NSF Biocomplexity in the Environment program (NSF EAR-0321918)

Repositionable Versus Balloon-Expandable Devices for Transcatheter Aortic Valve Implantation in Patients With Aortic Stenosis.

The safety and effectiveness of the fully repositionable LOTUS valve system as compared with the balloon-expandable Edwards SAPIEN 3 prosthesis for the treatment of aortic stenosis has not been evaluated to date. All patients undergoing transcatheter aortic valve implantation with the Edwards SAPIEN 3 or the LOTUS valve system were included into the Swiss Transcatheter Aortic Valve Implantation Registry. An adjusted analysis was performed to compare the early clinical safety outcome according to the Valve Academic Research Consortium-2 definition. Between February 2014 and September 2015, 140 and 815 patients were treated with the LOTUS and the Edwards SAPIEN 3 valve, respectively. There was no difference in crude and adjusted analyses of the early safety outcome between patients treated with LOTUS (14.3%) and those treated with Edwards SAPIEN 3 (14.6%) (crude hazard ratio, 0.97; 95% CI, 0.61-1.56 [P=0.915]; adjusted hazard ratio, 1.03; 95% CI, 0.64-1.67 [P=0.909]). More than mild aortic regurgitation was <2% for both devices. A total of 34.3% of patients treated with LOTUS and 14.1% of patients treated with Edwards SAPIEN 3 required a permanent pacemaker (HR, 2.76; 95% CI, 1.97-3.87 [P<0.001]). The repositionable LOTUS valve system and the balloon-expandable Edwards SAPIEN 3 prosthesis appeared comparable in regard to the Valve Academic Research Consortium-2 early safety outcome, and the rates of more than mild aortic regurgitation were exceedingly low for both devices. The need for new permanent pacemaker implantation was more frequent among patients treated with the LOTUS valve

Technical and Clinical Outcomes After Transcatheter Edge-to-Edge Repair of Mitral Regurgitation in Male and Female Patients: Is Equality Achieved?

Currently, no clear impact of sex on short- and long-term survival following transcatheter edge-to-edge mitral valve repair (TEER) is evident, although no data are available on postprocedural life expectancy. Our aim was to assess sex-specific differences in outcomes of patients with mitral regurgitation (MR) treated by TEER. Short-term and 5-year outcomes in men and women undergoing TEER between 2011 and 2018 who were included in the large, multicenter, real-world MitraSwiss registry were analyzed. Outcomes were compared stratified by sex and according to MR cause (primary versus secondary). The impact of TEER on postprocedural life expectancy was estimated by relative survival analysis. Among 1142 patients aged 60 to 89 years, 39.8% were women. They were older, with fewer cardiovascular risk factors and lower functional capacity compared with men. Thirty-day mortality was higher in men than in women (3.3% versus 1.1%; odds ratio, 3.16 [95% CI, 1.16-10.7]; P=0.020). Five-year survival was comparable in both sexes (adjusted hazard ratio for 5-year mortality in men, 1.14 [95% CI, 0.90-1.44], P=0.275). Both men and women with either primary or secondary MR showed similar clinical efficacy over time. TEER provided high relative survival estimates among all groups, and fully restored predicted life expectancy in women with primary MR (5-year relative survival estimate, 97.4% [95% CI, 85.5-107.0]). TEER is not associated with increased short-term mortality in women, whereas 5-year outcomes are comparable between sexes. Moreover, TEER completely restored normal life expectancy in women with primary MR. A residual excess mortality persists in secondary MR, independently of sex

Enhanced CO2 outgassing in the Southern Ocean from a positive phase of the Southern Annular Mode

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 21 (2007): GB2026, doi:10.1029/2006GB002900.We investigate the interannual variability in the flux of CO2 between the atmosphere and the Southern Ocean on the basis of hindcast simulations with a coupled physical-biogeochemical-ecological model with particular emphasis on the role of the Southern Annular Mode (SAM). The simulations are run under either pre-industrial or historical CO2 concentrations, permitting us to separately investigate natural, anthropogenic, and contemporary CO2 flux variability. We find large interannual variability (±0.19 PgC yr−1) in the contemporary air-sea CO2 flux from the Southern Ocean (<35°S). Forty-three percent of the contemporary air-sea CO2 flux variance is coherent with SAM, mostly driven by variations in the flux of natural CO2, for which SAM explains 48%. Positive phases of the SAM are associated with anomalous outgassing of natural CO2 at a rate of 0.1 PgC yr−1 per standard deviation of the SAM. In contrast, we find an anomalous uptake of anthropogenic CO2 at a rate of 0.01 PgC yr−1 during positive phases of the SAM. This uptake of anthropogenic CO2 only slightly mitigates the outgassing of natural CO2, so that a positive SAM is associated with anomalous outgassing in contemporaneous times. The primary cause of the natural CO2 outgassing is anomalously high oceanic partial pressures of CO2 caused by elevated dissolved inorganic carbon (DIC) concentrations. These anomalies in DIC are primarily a result of the circulation changes associated with the southward shift and strengthening of the zonal winds during positive phases of the SAM. The secular, positive trend in the SAM has led to a reduction in the rate of increase of the uptake of CO2 by the Southern Ocean over the past 50 years.This work was supported by NASA headquarters under the Earth System Science Fellowship Grant NNG05GP78H to N. S. L. and grants NAG5-12528 and NNG04GH53G to N. G. Both S. C. D. and I. D. L. were supported by NSF/ONR NOPP (N000140210370) and NASA (NNG05GG30G)

Evidence from diatom-bound nitrogen isotopes for subarctic Pacific stratification during the last ice age and a link to North Pacific denitrification changes

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 22 (2007): PA1215, doi:10.1029/2005PA001205.In a piston core from the central Bering Sea, diatom microfossil-bound N isotopes and the concentrations of opal, biogenic barium, calcium carbonate, and organic N are measured over the last glacial/interglacial cycle. Compared to the interglacial sections of the core, the sediments of the last ice age are characterized by 3‰ higher diatom-bound δ 15N, 70 wt % lower opal content and 1200 ppm lower biogenic barium. Taken together and with constraints on sediment accumulation rate, these results suggest a reduced supply of nitrate to the surface due to stronger stratification of the upper water column of the Bering Sea during glacial times, with more complete nitrate consumption resulting from continued iron supply through atmospheric deposition. This finding extends the body of evidence for a pervasive link between cold climates and polar ocean stratification. In addition, we hypothesize that more complete nutrient consumption in the glacial age subarctic Pacific contributed to the previously observed ice age reduction in suboxia and denitrification in the eastern tropical North Pacific by lowering the nutrient content of the intermediate-depth water formed in the subpolar North Pacific. In the deglacial interval of the Bering Sea record, two apparent peaks in export productivity are associated with maxima in diatom-bound and bulk sediment δ 15N. The high δ 15N in these intervals may have resulted from greater surface nutrient consumption during this period. However, the synchroneity of the deglacial peaks in the Bering Sea with similar bulk sediment δ 15N changes in the eastern Pacific margin and the presence of sediment lamination within the Bering Sea during the deposition of the productivity peaks raise the possibility that both regional and local denitrification worked to raise the δ 15N of the nitrate feeding Bering Sea surface waters at these times.Financial support for this work was provided by NSF grants OCE-0136449, OCE-9981479, ANT-0453680, by BP and Ford Motor Company through the Princeton Carbon Migration Initiative, and by a NDSEG fellowship to B.G.B. Work conducted aboard the USCG Healy (Healy 0202) was funded by grant OPP-9912122

Tropical Pacific climate response to obliquity forcing in the Pleistocene

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95532/1/palo1247.pd

The response of the Antarctic Circumpolar Current to recent climate change

Observations show a significant intensification of the Southern Hemisphere westerlies, the prevailing winds between the latitudes of 30° and 60° S, over the past decades. A continuation of this intensification trend is projected by climate scenarios for the twenty-first century. The response of the Antarctic Circumpolar Current and the carbon sink in the Southern Ocean to changes in wind stress and surface buoyancy fluxes is under debate. Here we analyse the Argo network of profiling floats and historical oceanographic data to detect coherent hemispheric-scale warming and freshening trends that extend to depths of more than 1,000 m. The warming and freshening is partly related to changes in the properties of the water masses that make up the Antarctic Circumpolar Current, which are consistent with the anthropogenic changes in heat and freshwater fluxes suggested by climate models. However, we detect no increase in the tilt of the surfaces of equal density across the Antarctic Circumpolar Current, in contrast to coarse-resolution model studies. Our results imply that the transport in the Antarctic Circumpolar Current and meridional overturning in the Southern Ocean are insensitive to decadal changes in wind stress