Publications by authors named "Gavin L Foster"

26 Publications

  • Page 1 of 1

Past climates inform our future.

Science 2020 11;370(6517)

Department of Oceanography, Texas A&M University, College Station, TX, USA.

As the world warms, there is a profound need to improve projections of climate change. Although the latest Earth system models offer an unprecedented number of features, fundamental uncertainties continue to cloud our view of the future. Past climates provide the only opportunity to observe how the Earth system responds to high carbon dioxide, underlining a fundamental role for paleoclimatology in constraining future climate change. Here, we review the relevancy of paleoclimate information for climate prediction and discuss the prospects for emerging methodologies to further insights gained from past climates. Advances in proxy methods and interpretations pave the way for the use of past climates for model evaluation-a practice that we argue should be widely adopted.
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http://dx.doi.org/10.1126/science.aay3701DOI Listing
November 2020

Author Correction: Long-term field comparison of multiple low-cost particulate matter sensors in an outdoor urban environment.

Sci Rep 2020 Oct 14;10(1):17670. Epub 2020 Oct 14.

Southampton Marine and Maritime Institute, University of Southampton, Southampton, UK.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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http://dx.doi.org/10.1038/s41598-020-74312-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7555530PMC
October 2020

Atmospheric CO during the Mid-Piacenzian Warm Period and the M2 glaciation.

Sci Rep 2020 07 9;10(1):11002. Epub 2020 Jul 9.

School of Ocean and Earth Science, University of Southampton, National Oceanography Centre Southampton,Waterfront Campus Southampton, Southampton, SO14 3ZH, UK.

The Piacenzian stage of the Pliocene (2.6 to 3.6 Ma) is the most recent past interval of sustained global warmth with mean global temperatures markedly higher (by ~2-3 °C) than today. Quantifying CO levels during the mid-Piacenzian Warm Period (mPWP) provides a means, therefore, to deepen our understanding of Earth System behaviour in a warm climate state. Here we present a new high-resolution record of atmospheric CO using the δB-pH proxy from 3.35 to 3.15 million years ago (Ma) at a temporal resolution of 1 sample per 3-6 thousand years (kyrs). Our study interval covers both the coolest marine isotope stage of the mPWP, M2 (~3.3 Ma) and the transition into its warmest phase including interglacial KM5c (centered on ~3.205 Ma) which has a similar orbital configuration to present. We find that CO ranged from [Formula: see text]ppm to [Formula: see text]ppm, with CO during the KM5c interglacial being [Formula: see text]ppm (at 95% confidence). Our findings corroborate the idea that changes in atmospheric CO levels played a distinct role in climate variability during the mPWP. They also facilitate ongoing data-model comparisons and suggest that, at present rates of human emissions, there will be more CO in Earth's atmosphere by 2025 than at any time in at least the last 3.3 million years.
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http://dx.doi.org/10.1038/s41598-020-67154-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7347535PMC
July 2020

Automation of boron chromatographic purification for δ B analysis of coral aragonite.

Rapid Commun Mass Spectrom 2020 Jun;34(11):e8762

School of Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Southampton, SO14 3ZH, UK.

Rationale: To detect the small changes in past pH the boron isotope ratio of coral carbonates, expressed as the δ B value, needs to be both precise and accurate (2sd <1‰). Boron measurements by Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS) require the boron to be carefully purified before analysis, which is time consuming, and requires specialist training. Here, we use the prepFAST-MC method that enables the automatic extraction of B (up to 25 ng load) from a CaCO matrix.

Methods: Samples were purified using the prepFAST-MC automated system with a ~25-μL column of Amberlite IRA743 resin. Boron isotope measurements were performed by MC-ICPMS. The effects of matrix load, speed of sample loading onto the column, and blank contamination were tested to evaluate the effects on the purification process. The optimised protocol was tested on various standards and samples of aragonite corals.

Results: The blank contribution for the approach is ~60 pg and is negligible given our sample size (<0.2% sample size). Efficiency of matrix removal is demonstrated with the addition of up to 1.6 mg of dissolved low-B calcium carbonate to NIST SRM 951 with no impact on the accuracy of δ B values. The Japanese Geological Survey Porites reference material JCp-1, boric acid standard NIST SRM 951, and seawater, all processed on the prepFAST-MC system, give δ B values within error of literature values (δ B = 24.31 ± 0.20‰ (2sd, n = 20); δ B = -0.02 ± 0.15‰ (2sd, n = 13) and δ B = 39.50 ± 0.06‰ (2sd, n = 2)). Results obtained from the coral Siderastrea siderea purified with the prepFAST-MC system show an average offset from the manual ion-exchange protocols of Δδ B = 0.01 ± 0.28‰ (2sd, n = 12).

Conclusions: Our study demonstrates the capacity of the prepFAST-MC method to generate accurate and reproducible δ B values for a range of materials, without fractionation, with efficient matrix removal and with negligible blank contribution.
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http://dx.doi.org/10.1002/rcm.8762DOI Listing
June 2020

Long-term field comparison of multiple low-cost particulate matter sensors in an outdoor urban environment.

Sci Rep 2019 05 16;9(1):7497. Epub 2019 May 16.

Southampton Marine and Maritime Institute, University of Southampton, Southampton, UK.

Exposure to ambient particulate matter (PM) air pollution is a leading risk factor for morbidity and mortality, associated with up to 8.9 million deaths/year worldwide. Measurement of personal exposure to PM is hindered by poor spatial resolution of monitoring networks. Low-cost PM sensors may improve monitoring resolution in a cost-effective manner but there are doubts regarding data reliability. PM sensor boxes were constructed using four low-cost PM micro-sensor models. Three boxes were deployed at each of two schools in Southampton, UK, for around one year and sensor performance was analysed. Comparison of sensor readings with a nearby background station showed moderate to good correlation (0.61 < r < 0.88, p < 0.0001), but indicated that low-cost sensor performance varies with different PM sources and background concentrations, and to a lesser extent relative humidity and temperature. This may have implications for their potential use in different locations. Data also indicates that these sensors can track short-lived events of pollution, especially in conjunction with wind data. We conclude that, with appropriate consideration of potential confounding factors, low-cost PM sensors may be suitable for PM monitoring where reference-standard equipment is not available or feasible, and that they may be useful in studying spatially localised airborne PM concentrations.
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http://dx.doi.org/10.1038/s41598-019-43716-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6522472PMC
May 2019

The effect of matrix interferences on in situ boron isotope analysis by laser ablation multi-collector inductively coupled plasma mass spectrometry.

Rapid Commun Mass Spectrom 2019 May;33(10):959-968

School of Ocean and Earth Science, University of Southampton Waterfront Campus, National Oceanography Centre Southampton, European Way, Southampton, SO14 3ZH, UK.

Rationale: Boron isotope analysis of marine carbonates by laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) offers the potential for rapid sample throughput, and the means to examine micron-scale variations in the δ B signatures of fossil skeletons and shells/tests of marine organisms. Existing studies demonstrate an acceptable level of reproducibility is achievable, but also typically show a level of accuracy outside the limits required by most applications. Here we investigate matrix interference effects as a cause of inaccuracy and imprecision.

Methods: Analyses were performed on a standard format Thermo Scientific Neptune Plus MC-ICP mass spectrometer coupled to a New Wave Research 193 nm ArF laser ablation system. The effects of matrix interference on δ B analysis were investigated through analyses of a set of reference materials with differing B/Ca ratios. Three approaches to correct for matrix-induced effects were trialled: (1) use of matrix-matched standards, (2) utilisation of the relationship between δ B inaccuracy and B/ Ca, B/ ArCa or B/Ca from three reference materials with known δ B values and varying B/Ca ratios, and (3) direct characterisation of the (sloping) interference itself.

Results: Matrix interference from scattered Ca ions on B can impede both the accuracy and the reproducibility of δ B analysis by LA-MC-ICP-MS. Based on analyses of two in-house reference materials, deep sea coral PS69/3181 and inorganic calcite UWC-1, we find approach 2, following the B/Ca relationship, gives the best mean accuracies (within 0.4‰ of solution values) and external reproducibilities (± 0.5‰ 2 SD for PS69/3181). This approach has been applied to analyses of an annual growth cycle of a Siderastrea siderea coral and eight Cibicidoides wuellerstorfi benthic foraminifera. Both coral and foraminifera data match solution MC-ICP-MS analyses within reported uncertainties.

Conclusions: LA-MC-ICP-MS can produce accurate and precise δ B data to a 0.5‰ (2σ) level on <0.3 ng B after correction for Ca interference effects.
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http://dx.doi.org/10.1002/rcm.8432DOI Listing
May 2019

City Scale Particulate Matter Monitoring Using LoRaWAN Based Air Quality IoT Devices.

Sensors (Basel) 2019 Jan 8;19(1). Epub 2019 Jan 8.

Faculty of Engineering and Physical Sciences, University of Southampton, Southampton SO16 7QF, UK.

Air Quality (AQ) is a very topical issue for many cities and has a direct impact on citizen health. The AQ of a large UK city is being investigated using low-cost Particulate Matter (PM) sensors, and the results obtained by these sensors have been compared with government operated AQ stations. In the first pilot deployment, six AQ Internet of Things (IoT) devices have been designed and built, each with four different low-cost PM sensors, and they have been deployed at two locations within the city. These devices are equipped with LoRaWAN wireless network transceivers to test city scale Low-Power Wide Area Network (LPWAN) coverage. The study concludes that (i) the physical device developed can operate at a city scale; (ii) some low-cost PM sensors are viable for monitoring AQ and for detecting PM trends; (iii) LoRaWAN is suitable for city scale sensor coverage where connectivity is an issue. Based on the findings from this first pilot project, a larger LoRaWAN enabled AQ sensor network is being deployed across the city of Southampton in the UK.
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http://dx.doi.org/10.3390/s19010209DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6339063PMC
January 2019

Placing our current 'hyperthermal' in the context of rapid climate change in our geological past.

Philos Trans A Math Phys Eng Sci 2018 Oct;376(2130)

Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, CA 95064, USA.

'…there are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don't know. But there are also unknown unknowns. There are things we don't know we don't know.' Donald Rumsfeld 12th February 2002.This article is part of a discussion meeting issue 'Hyperthermals: rapid and extreme global warming in our geological past'.
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http://dx.doi.org/10.1098/rsta.2017.0086DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6127387PMC
October 2018

No substantial long-term bias in the Cenozoic benthic foraminifera oxygen-isotope record.

Nat Commun 2018 07 23;9(1):2875. Epub 2018 Jul 23.

Department of Earth and Planetary Sciences, University of California, Santa Cruz, 95064, CA, USA.

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http://dx.doi.org/10.1038/s41467-018-05303-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6056492PMC
July 2018

Ocean acidification affects coral growth by reducing skeletal density.

Proc Natl Acad Sci U S A 2018 02 29;115(8):1754-1759. Epub 2018 Jan 29.

Marine Policy Center, Woods Hole Oceanographic Institution, Woods Hole, MA 02543.

Ocean acidification (OA) is considered an important threat to coral reef ecosystems, because it reduces the availability of carbonate ions that reef-building corals need to produce their skeletons. However, while theory predicts that coral calcification rates decline as carbonate ion concentrations decrease, this prediction is not consistently borne out in laboratory manipulation experiments or in studies of corals inhabiting naturally low-pH reefs today. The skeletal growth of corals consists of two distinct processes: extension (upward growth) and densification (lateral thickening). Here, we show that skeletal density is directly sensitive to changes in seawater carbonate ion concentration and thus, to OA, whereas extension is not. We present a numerical model of skeletal growth that links skeletal density with the external seawater environment via its influence on the chemistry of coral calcifying fluid. We validate the model using existing coral skeletal datasets from six species collected across five reef sites and use this framework to project the impact of 21st century OA on skeletal density across the global tropics. Our model predicts that OA alone will drive up to 20.3 ± 5.4% decline in the skeletal density of reef-building corals.
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http://dx.doi.org/10.1073/pnas.1712806115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5828584PMC
February 2018

Causes of ice age intensification across the Mid-Pleistocene Transition.

Proc Natl Acad Sci U S A 2017 12 27;114(50):13114-13119. Epub 2017 Nov 27.

Ocean and Earth Science, University of Southampton, National Oceanography Centre Southampton, Southampton SO14 3ZH, United Kingdom.

During the Mid-Pleistocene Transition (MPT; 1,200-800 kya), Earth's orbitally paced ice age cycles intensified, lengthened from ∼40,000 (∼40 ky) to ∼100 ky, and became distinctly asymmetrical. Testing hypotheses that implicate changing atmospheric CO levels as a driver of the MPT has proven difficult with available observations. Here, we use orbitally resolved, boron isotope CO data to show that the glacial to interglacial CO difference increased from ∼43 to ∼75 μatm across the MPT, mainly because of lower glacial CO levels. Through carbon cycle modeling, we attribute this decline primarily to the initiation of substantive dust-borne iron fertilization of the Southern Ocean during peak glacial stages. We also observe a twofold steepening of the relationship between sea level and CO-related climate forcing that is suggestive of a change in the dynamics that govern ice sheet stability, such as that expected from the removal of subglacial regolith or interhemispheric ice sheet phase-locking. We argue that neither ice sheet dynamics nor CO change in isolation can explain the MPT. Instead, we infer that the MPT was initiated by a change in ice sheet dynamics and that longer and deeper post-MPT ice ages were sustained by carbon cycle feedbacks related to dust fertilization of the Southern Ocean as a consequence of larger ice sheets.
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http://dx.doi.org/10.1073/pnas.1702143114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5740680PMC
December 2017

Comparing Climate Sensitivity, Past and Present.

Ann Rev Mar Sci 2018 01 22;10:261-288. Epub 2017 Sep 22.

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar-und Meeresforschung (AWI), 27515 Bremerhaven, Germany; email:

Climate sensitivity represents the global mean temperature change caused by changes in the radiative balance of climate; it is studied for both present/future (actuo) and past (paleo) climate variations, with the former based on instrumental records and/or various types of model simulations. Paleo-estimates are often considered informative for assessments of actuo-climate change caused by anthropogenic greenhouse forcing, but this utility remains debated because of concerns about the impacts of uncertainties, assumptions, and incomplete knowledge about controlling mechanisms in the dynamic climate system, with its multiple interacting feedbacks and their potential dependence on the climate background state. This is exacerbated by the need to assess actuo- and paleoclimate sensitivity over different timescales, with different drivers, and with different (data and/or model) limitations. Here, we visualize these impacts with idealized representations that graphically illustrate the nature of time-dependent actuo- and paleoclimate sensitivity estimates, evaluating the strengths, weaknesses, agreements, and differences of the two approaches. We also highlight priorities for future research to improve the use of paleo-estimates in evaluations of current climate change.
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http://dx.doi.org/10.1146/annurev-marine-121916-063242DOI Listing
January 2018

Very large release of mostly volcanic carbon during the Palaeocene-Eocene Thermal Maximum.

Nature 2017 08;548(7669):573-577

Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Southampton SO17 1BJ, UK.

The Palaeocene-Eocene Thermal Maximum (PETM) was a global warming event that occurred about 56 million years ago, and is commonly thought to have been driven primarily by the destabilization of carbon from surface sedimentary reservoirs such as methane hydrates. However, it remains controversial whether such reservoirs were indeed the source of the carbon that drove the warming. Resolving this issue is key to understanding the proximal cause of the warming, and to quantifying the roles of triggers versus feedbacks. Here we present boron isotope data-a proxy for seawater pH-that show that the ocean surface pH was persistently low during the PETM. We combine our pH data with a paired carbon isotope record in an Earth system model in order to reconstruct the unfolding carbon-cycle dynamics during the event. We find strong evidence for a much larger (more than 10,000 petagrams)-and, on average, isotopically heavier-carbon source than considered previously. This leads us to identify volcanism associated with the North Atlantic Igneous Province, rather than carbon from a surface reservoir, as the main driver of the PETM. This finding implies that climate-driven amplification of organic carbon feedbacks probably played only a minor part in driving the event. However, we find that enhanced burial of organic matter seems to have been important in eventually sequestering the released carbon and accelerating the recovery of the Earth system.
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http://dx.doi.org/10.1038/nature23646DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5582631PMC
August 2017

Future climate forcing potentially without precedent in the last 420 million years.

Nat Commun 2017 04 4;8:14845. Epub 2017 Apr 4.

School of Geographical Sciences and Cabot Institute, University of Bristol, University Road, Bristol BS8 1SS, UK.

The evolution of Earth's climate on geological timescales is largely driven by variations in the magnitude of total solar irradiance (TSI) and changes in the greenhouse gas content of the atmosphere. Here we show that the slow ∼50 Wm increase in TSI over the last ∼420 million years (an increase of ∼9 Wm of radiative forcing) was almost completely negated by a long-term decline in atmospheric CO. This was likely due to the silicate weathering-negative feedback and the expansion of land plants that together ensured Earth's long-term habitability. Humanity's fossil-fuel use, if unabated, risks taking us, by the middle of the twenty-first century, to values of CO not seen since the early Eocene (50 million years ago). If CO continues to rise further into the twenty-third century, then the associated large increase in radiative forcing, and how the Earth system would respond, would likely be without geological precedent in the last half a billion years.
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http://dx.doi.org/10.1038/ncomms14845DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5382278PMC
April 2017

Changing atmospheric CO2 concentration was the primary driver of early Cenozoic climate.

Nature 2016 05 25;533(7603):380-4. Epub 2016 Apr 25.

School of Earth and Ocean Sciences, Cardiff University, Park Place, Cardiff CF10 3AT, UK.

The Early Eocene Climate Optimum (EECO, which occurred about 51 to 53 million years ago), was the warmest interval of the past 65 million years, with mean annual surface air temperature over ten degrees Celsius warmer than during the pre-industrial period. Subsequent global cooling in the middle and late Eocene epoch, especially at high latitudes, eventually led to continental ice sheet development in Antarctica in the early Oligocene epoch (about 33.6 million years ago). However, existing estimates place atmospheric carbon dioxide (CO2) levels during the Eocene at 500-3,000 parts per million, and in the absence of tighter constraints carbon-climate interactions over this interval remain uncertain. Here we use recent analytical and methodological developments to generate a new high-fidelity record of CO2 concentrations using the boron isotope (δ(11)B) composition of well preserved planktonic foraminifera from the Tanzania Drilling Project, revising previous estimates. Although species-level uncertainties make absolute values difficult to constrain, CO2 concentrations during the EECO were around 1,400 parts per million. The relative decline in CO2 concentration through the Eocene is more robustly constrained at about fifty per cent, with a further decline into the Oligocene. Provided the latitudinal dependency of sea surface temperature change for a given climate forcing in the Eocene was similar to that of the late Quaternary period, this CO2 decline was sufficient to drive the well documented high- and low-latitude cooling that occurred through the Eocene. Once the change in global temperature between the pre-industrial period and the Eocene caused by the action of all known slow feedbacks (apart from those associated with the carbon cycle) is removed, both the EECO and the late Eocene exhibit an equilibrium climate sensitivity relative to the pre-industrial period of 2.1 to 4.6 degrees Celsius per CO2 doubling (66 per cent confidence), which is similar to the canonical range (1.5 to 4.5 degrees Celsius), indicating that a large fraction of the warmth of the early Eocene greenhouse was driven by increased CO2 concentrations, and that climate sensitivity was relatively constant throughout this period.
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http://dx.doi.org/10.1038/nature17423DOI Listing
May 2016

Lessons on Climate Sensitivity From Past Climate Changes.

Curr Clim Change Rep 2016 20;2(4):148-158. Epub 2016 Oct 20.

24Department of Earth Sciences, Utrecht University, PO Box 80.021, 3508 TA Utrecht, The Netherlands.

Over the last decade, our understanding of climate sensitivity has improved considerably. The climate system shows variability on many timescales, is subject to non-stationary forcing and it is most likely out of equilibrium with the changes in the radiative forcing. Slow and fast feedbacks complicate the interpretation of geological records as feedback strengths vary over time. In the geological past, the forcing timescales were different than at present, suggesting that the response may have behaved differently. Do these insights constrain the climate sensitivity relevant for the present day? In this paper, we review the progress made in theoretical understanding of climate sensitivity and on the estimation of climate sensitivity from proxy records. Particular focus lies on the background state dependence of feedback processes and on the impact of tipping points on the climate system. We suggest how to further use palaeo data to advance our understanding of the currently ongoing climate change.
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http://dx.doi.org/10.1007/s40641-016-0049-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6979625PMC
October 2016

A geological perspective on potential future sea-level rise.

Sci Rep 2013 Dec 12;3:3461. Epub 2013 Dec 12.

1] Research School of Earth Sciences, The Australian National University, Canberra 0200 Australia [2] Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton SO14 3ZH, UK.

During ice-age cycles, continental ice volume kept pace with slow, multi-millennial scale, changes in climate forcing. Today, rapid greenhouse gas (GHG) increases have outpaced ice-volume responses, likely committing us to > 9 m of long-term sea-level rise (SLR). We portray a context of naturally precedented SLR from geological evidence, for comparison with historical observations and future projections. This context supports SLR of up to 0.9 (1.8) m by 2100 and 2.7 (5.0) m by 2200, relative to 2000, at 68% (95%) probability. Historical SLR observations and glaciological assessments track the upper 68% limit. Hence, modern change is rapid by past interglacial standards but within the range of 'normal' processes. The upper 95% limit offers a useful low probability/high risk value. Exceedance would require conditions without natural interglacial precedents, such as catastrophic ice-sheet collapse, or activation of major East Antarctic mass loss at sustained CO2 levels above 1000 ppmv.
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http://dx.doi.org/10.1038/srep03461DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3860070PMC
December 2013

Warm ocean processes and carbon cycling in the Eocene.

Philos Trans A Math Phys Eng Sci 2013 Oct 16;371(2001):20130099. Epub 2013 Sep 16.

School of Earth and Ocean Sciences, Cardiff University, , Park Place, Cardiff CF10 3AT, UK.

Sea surface and subsurface temperatures over large parts of the ocean during the Eocene epoch (55.5-33.7 Ma) exceeded modern values by several degrees, which must have affected a number of oceanic processes. Here, we focus on the effect of elevated water column temperatures on the efficiency of the biological pump, particularly in relation to carbon and nutrient cycling. We use stable isotope values from exceptionally well-preserved planktonic foraminiferal calcite from Tanzania and Mexico to reconstruct vertical carbon isotope gradients in the upper water column, exploiting the fact that individual species lived and calcified at different depths. The oxygen isotope ratios of different species' tests are used to estimate the temperature of calcification, which we converted to absolute depths using Eocene temperature profiles generated by general circulation models. This approach, along with potential pitfalls, is illustrated using data from modern core-top assemblages from the same area. Our results indicate that, during the Early and Middle Eocene, carbon isotope gradients were steeper (and larger) through the upper thermocline than in the modern ocean. This is consistent with a shallower average depth of organic matter remineralization and supports previously proposed hypotheses that invoke high metabolic rates in a warm Eocene ocean, leading to more efficient recycling of organic matter and reduced burial rates of organic carbon.
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http://dx.doi.org/10.1098/rsta.2013.0099DOI Listing
October 2013

Relationship between sea level and climate forcing by CO2 on geological timescales.

Proc Natl Acad Sci U S A 2013 Jan 4;110(4):1209-14. Epub 2013 Jan 4.

Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton Waterfront Campus, Southampton SO14 3ZH, United Kingdom.

On 10(3)- to 10(6)-year timescales, global sea level is determined largely by the volume of ice stored on land, which in turn largely reflects the thermal state of the Earth system. Here we use observations from five well-studied time slices covering the last 40 My to identify a well-defined and clearly sigmoidal relationship between atmospheric CO(2) and sea level on geological (near-equilibrium) timescales. This strongly supports the dominant role of CO(2) in determining Earth's climate on these timescales and suggests that other variables that influence long-term global climate (e.g., topography, ocean circulation) play a secondary role. The relationship between CO(2) and sea level we describe portrays the "likely" (68% probability) long-term sea-level response after Earth system adjustment over many centuries. Because it appears largely independent of other boundary condition changes, it also may provide useful long-range predictions of future sea level. For instance, with CO(2) stabilized at 400-450 ppm (as required for the frequently quoted "acceptable warming" of 2 °C), or even at AD 2011 levels of 392 ppm, we infer a likely (68% confidence) long-term sea-level rise of more than 9 m above the present. Therefore, our results imply that to avoid significantly elevated sea level in the long term, atmospheric CO(2) should be reduced to levels similar to those of preindustrial times.
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http://dx.doi.org/10.1073/pnas.1216073110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3557064PMC
January 2013

A Cenozoic record of the equatorial Pacific carbonate compensation depth.

Nature 2012 Aug;488(7413):609-14

Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Waterfront Campus, European Way, Southampton SO14 3ZH, UK.

Atmospheric carbon dioxide concentrations and climate are regulated on geological timescales by the balance between carbon input from volcanic and metamorphic outgassing and its removal by weathering feedbacks; these feedbacks involve the erosion of silicate rocks and organic-carbon-bearing rocks. The integrated effect of these processes is reflected in the calcium carbonate compensation depth, which is the oceanic depth at which calcium carbonate is dissolved. Here we present a carbonate accumulation record that covers the past 53 million years from a depth transect in the equatorial Pacific Ocean. The carbonate compensation depth tracks long-term ocean cooling, deepening from 3.0-3.5 kilometres during the early Cenozoic (approximately 55 million years ago) to 4.6 kilometres at present, consistent with an overall Cenozoic increase in weathering. We find large superimposed fluctuations in carbonate compensation depth during the middle and late Eocene. Using Earth system models, we identify changes in weathering and the mode of organic-carbon delivery as two key processes to explain these large-scale Eocene fluctuations of the carbonate compensation depth.
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http://dx.doi.org/10.1038/nature11360DOI Listing
August 2012

The geological record of ocean acidification.

Science 2012 Mar;335(6072):1058-63

Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USA.

Ocean acidification may have severe consequences for marine ecosystems; however, assessing its future impact is difficult because laboratory experiments and field observations are limited by their reduced ecologic complexity and sample period, respectively. In contrast, the geological record contains long-term evidence for a variety of global environmental perturbations, including ocean acidification plus their associated biotic responses. We review events exhibiting evidence for elevated atmospheric CO(2), global warming, and ocean acidification over the past ~300 million years of Earth's history, some with contemporaneous extinction or evolutionary turnover among marine calcifiers. Although similarities exist, no past event perfectly parallels future projections in terms of disrupting the balance of ocean carbonate chemistry-a consequence of the unprecedented rapidity of CO(2) release currently taking place.
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http://dx.doi.org/10.1126/science.1208277DOI Listing
March 2012

Atmospheric carbon dioxide through the Eocene-Oligocene climate transition.

Nature 2009 Oct 13;461(7267):1110-3. Epub 2009 Sep 13.

School of Earth and Ocean Sciences, Cardiff University, Cardiff CF10 3YE, UK.

Geological and geochemical evidence indicates that the Antarctic ice sheet formed during the Eocene-Oligocene transition, 33.5-34.0 million years ago. Modelling studies suggest that such ice-sheet formation might have been triggered when atmospheric carbon dioxide levels (pCO2atm) fell below a critical threshold of approximately 750 p.p.m.v., but the timing and magnitude of pCO2atm relative to the evolution of the ice sheet has remained unclear. Here we use the boron isotope pH proxy on exceptionally well-preserved carbonate microfossils from a recently discovered geological section in Tanzania to estimate pCO2atm before, during and after the climate transition. Our data suggest that are reduction in pCO2atm occurred before the main phase of ice growth,followed by a sharp recovery to pre-transition values and then a more gradual decline. During maximum ice-sheet growth, pCO2atm was between approximately 450 and approximately 1,500 p.p.m.v., with a central estimate of approximately 760 p.p.m.v. The ice cap survived the period of pCO2atm recovery,although possibly with some reduction in its volume, implying (as models predict) a nonlinear response to climate forcing during melting. Overall, our results confirm the central role of declining pCO2atm in the development of the Antarctic ice sheet (in broad agreement with carbon cycle modelling) and help to constrain mechanisms and feedbacks associated with the Earth's biggest climate switch of the past 65 Myr.
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http://dx.doi.org/10.1038/nature08447DOI Listing
October 2009

Variable Quaternary chemical weathering fluxes and imbalances in marine geochemical budgets.

Nature 2009 Mar;458(7237):493-6

Bristol Isotope Group, Department of Earth Sciences, University of Bristol, Wills Memorial Building, Bristol BS8 1RJ, UK.

Rivers are the dominant source of many elements and isotopes to the ocean. But this input from the continents is not balanced by the loss of the elements and isotopes through hydrothermal and sedimentary exchange with the oceanic crust, or by temporal changes in the marine inventory for elements that are demonstrably not in steady state. To resolve the problem of the observed imbalance in marine geochemical budgets, attention has been focused on uncertainties in the hydrothermal and sedimentary fluxes. In recent Earth history, temporally dynamic chemical weathering fluxes from the continents are an inevitable consequence of periodic glaciations. Chemical weathering rates on modern Earth are likely to remain far from equilibrium owing to the physical production of finely ground material at glacial terminations that acts as a fertile substrate for chemical weathering. Here we explore the implications of temporal changes in the riverine chemical weathering flux for oceanic geochemical budgets. We contend that the riverine flux obtained from observations of modern rivers is broadly accurate, but not representative of timescales appropriate for elements with oceanic residence longer than Quaternary glacial-interglacial cycles. We suggest that the pulse of rapid chemical weathering initiated at the last deglaciation has not yet decayed away and that weathering rates remain about two to three times the average for an entire late Quaternary glacial cycle. Taking into account the effect of the suggested non-steady-state process on the silicate weathering flux helps to reconcile the modelled marine strontium isotope budget with available data. Overall, we conclude that consideration of the temporal variability in riverine fluxes largely ameliorates long-standing problems with chemical and isotopic mass balances in the ocean.
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http://dx.doi.org/10.1038/nature07828DOI Listing
March 2009

The Arctic cryosphere in the Mid-Pliocene and the future.

Philos Trans A Math Phys Eng Sci 2009 Jan;367(1886):49-67

BRIDGE, School of Geographical Sciences, University of Bristol, Bristol BS8 1SS, UK.

The Mid-Pliocene (ca 3Myr ago) was a relatively warm period, with increased atmospheric CO2 relative to pre-industrial. It has therefore been highlighted as a possible palaeo-analogue for the future. However, changed vegetation patterns, orography and smaller ice sheets also influenced the Mid-Pliocene climate. Here, using a general circulation model and ice-sheet model, we determine the relative contribution of vegetation and soils, orography and ice, and CO2 to the Mid-Pliocene Arctic climate and cryosphere. Compared with pre-industrial, we find that increased Mid-Pliocene CO2 contributes 35 per cent, lower orography and ice-sheet feedbacks contribute 42 per cent, and vegetation changes contribute 23 per cent of Arctic temperature change. The simulated Mid-Pliocene Greenland ice sheet is substantially smaller than that of modern, mostly due to the higher CO2. However, our simulations of future climate change indicate that the same increase in CO2 is not sufficient to melt the modern ice sheet substantially. We conclude that, although the Mid-Pliocene resembles the future in some respects, care must be taken when interpreting it as an exact analogue due to vegetation and ice-sheet feedbacks. These act to intensify Mid-Pliocene Arctic climate change, and act on a longer time scale than the century scale usually addressed in future climate prediction.
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http://dx.doi.org/10.1098/rsta.2008.0218DOI Listing
January 2009

Late Pliocene Greenland glaciation controlled by a decline in atmospheric CO2 levels.

Nature 2008 Aug;454(7208):1102-5

BRIDGE, School of Geographical Sciences, University of Bristol, University Road, Bristol BS8 1SS, UK.

It is thought that the Northern Hemisphere experienced only ephemeral glaciations from the Late Eocene to the Early Pliocene epochs (about 38 to 4 million years ago), and that the onset of extensive glaciations did not occur until about 3 million years ago. Several hypotheses have been proposed to explain this increase in Northern Hemisphere glaciation during the Late Pliocene. Here we use a fully coupled atmosphere-ocean general circulation model and an ice-sheet model to assess the impact of the proposed driving mechanisms for glaciation and the influence of orbital variations on the development of the Greenland ice sheet in particular. We find that Greenland glaciation is mainly controlled by a decrease in atmospheric carbon dioxide during the Late Pliocene. By contrast, our model results suggest that climatic shifts associated with the tectonically driven closure of the Panama seaway, with the termination of a permanent El Niño state or with tectonic uplift are not large enough to contribute significantly to the growth of the Greenland ice sheet; moreover, we find that none of these processes acted as a priming mechanism for glacial inception triggered by variations in the Earth's orbit.
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http://dx.doi.org/10.1038/nature07223DOI Listing
August 2008

Negligible glacial-interglacial variation in continental chemical weathering rates.

Nature 2006 Dec;444(7121):918-21

Bristol Isotope Group, Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK.

Chemical weathering of the continents is central to the regulation of atmospheric carbon dioxide concentrations, and hence global climate. On million-year timescales silicate weathering leads to the draw-down of carbon dioxide, and on millennial timescales chemical weathering affects the calcium carbonate saturation state of the oceans and hence their uptake of carbon dioxide. However, variations in chemical weathering rates over glacial-interglacial cycles remain uncertain. During glacial periods, cold and dry conditions reduce the rate of chemical weathering, but intense physical weathering and the exposure of carbonates on continental shelves due to low sea levels may increase this rate. Here we present high-resolution records of the lead isotope composition of ferromanganese crusts from the North Atlantic Ocean that cover the past 550,000 years. Combining these records with a simple quantitative model of changes in the lead isotope composition of the deep North Atlantic Ocean in response to chemical weathering, we find that chemical weathering rates were two to three times lower in the glaciated interior of the North Atlantic Region during glacial periods than during the intervening interglacial periods. This decrease roughly balances the increase in chemical weathering caused by the exposure of continental shelves, indicating that chemical weathering rates remained relatively constant on glacial-interglacial timescales. On timescales of more than a million years, however, we suggest that enhanced weathering of silicate glacial sediments during interglacial periods results in a net draw-down of atmospheric carbon dioxide, creating a positive feedback on global climate that, once initiated, promotes cooling and further glaciation.
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http://dx.doi.org/10.1038/nature05365DOI Listing
December 2006