Galen A. McKinley

Bio: Galen A. McKinley is an academic researcher from Lamont–Doherty Earth Observatory. The author has contributed to research in topics: Carbon sink & Carbon cycle. The author has an hindex of 31, co-authored 81 publications receiving 3776 citations. Previous affiliations of Galen A. McKinley include Courant Institute of Mathematical Sciences & Massachusetts Institute of Technology.

Constraining global air-sea gas exchange for CO2 with recent bomb 14C measurements

Abstract: [1] The 14CO2 released into the stratosphere during bomb testing in the early 1960s provides a global constraint on air-sea gas exchange of soluble atmospheric gases like CO2. Using the most complete database of dissolved inorganic radiocarbon, DI14C, available to date and a suite of ocean general circulation models in an inverse mode we recalculate the ocean inventory of bomb-produced DI14C in the global ocean and confirm that there is a 25% decrease from previous estimates using older DI14C data sets. Additionally, we find a 33% lower globally averaged gas transfer velocity for CO2 compared to previous estimates (Wanninkhof, 1992) using the NCEP/NCAR Reanalysis 1 1954–2000 where the global mean winds are 6.9 m s−1. Unlike some earlier ocean radiocarbon studies, the implied gas transfer velocity finally closes the gap between small-scale deliberate tracer studies and global-scale estimates. Additionally, the total inventory of bomb-produced radiocarbon in the ocean is now in agreement with global budgets based on radiocarbon measurements made in the stratosphere and troposphere. Using the implied relationship between wind speed and gas transfer velocity ks = 0.27〈u102〉(Sc/660)−0.5 and standard partial pressure difference climatology of CO2 we obtain an net air-sea flux estimate of 1.3 ± 0.5 PgCyr−1 for 1995. After accounting for the carbon transferred from rivers to the deep ocean, our estimate of oceanic uptake (1.8 ± 0.5 PgCyr−1) compares well with estimates based on ocean inventories, ocean transport inversions using ocean concentration data, and model simulations.

Global ocean storage of anthropogenic carbon

Abstract: The global ocean is a significant sink for anthropogenic carbon (C-ant), absorbing roughly a third of human CO2 emitted over the industrial period. Robust estimates of the magnitude and variability of the storage and distribution of C-ant in the ocean are therefore important for understanding the human impact on climate. In this synthesis we review observational and model-based estimates of the storage and transport of C-ant in the ocean. We pay particular attention to the uncertainties and potential biases inherent in different inference schemes. On a global scale, three data-based estimates of the distribution and inventory of C-ant are now available. While the inventories are found to agree within their uncertainty, there are considerable differences in the spatial distribution. We also present a review of the progress made in the application of inverse and data assimilation techniques which combine ocean interior estimates of C-ant with numerical ocean circulation models. Such methods are especially useful for estimating the air-sea flux and interior transport of C-ant, quantities that are otherwise difficult to observe directly. However, the results are found to be highly dependent on modeled circulation, with the spread due to different ocean models at least as large as that from the different observational methods used to estimate C-ant. Our review also highlights the importance of repeat measurements of hydro-graphic and biogeochemical parameters to estimate the storage of C-ant on decadal timescales in the presence of the variability in circulation that is neglected by other approaches. Data-based C-ant estimates provide important constraints on forward ocean models, which exhibit both broad similarities and regional errors relative to the observational fields. A compilation of inventories of C-ant gives us a "best" estimate of the global ocean inventory of anthropogenic carbon in 2010 of 155 +/- 31 PgC (+/- 20% uncertainty). This estimate includes a broad range of values, suggesting that a combination of approaches is necessary in order to achieve a robust quantification of the ocean sink of anthropogenic CO2.

Global ocean carbon uptake: magnitude, variability and trends

Abstract: The globally integrated sea–air anthropogenic carbon dioxide (CO 2 ) flux from 1990 to 2009 is determined from models and data-based approaches as part of the Regional Carbon Cycle Assessment and Processes (RECCAP) project. Numerical methods include ocean inverse models, atmospheric inverse models, and ocean general circulation models with parameterized biogeochemistry (OBGCMs). The median value of different approaches shows good agreement in average uptake. The best estimate of anthropogenic CO 2 uptake for the time period based on a compilation of approaches is −2.0 Pg C yr −1 . The interannual variability in the sea–air flux is largely driven by large-scale climate re-organizations and is estimated at 0.2 Pg C yr −1 for the two decades with some systematic differences between approaches. The largest differences between approaches are seen in the decadal trends. The trends range from −0.13 (Pg C yr −1 ) decade −1 to −0.50 (Pg C yr −1 ) decade −1 for the two decades under investigation. The OBGCMs and the data-based sea–air CO 2 flux estimates show appreciably smaller decadal trends than estimates based on changes in carbon inventory suggesting that methods capable of resolving shorter timescales are showing a slowing of the rate of ocean CO 2 uptake. RECCAP model outputs for five decades show similar differences in trends between approaches.

Multiple constraints on regional CO2 flux variations over land and oceans

Abstract: [1] To increase our understanding of the carbon cycle, we compare regional estimates of CO2 flux variability for 1980–1998 from atmospheric CO2 inversions and from process-based models of the land (SLAVE and LPJ) and ocean (OPA and MIT) Over the land, the phase and amplitude of the different estimates agree well, especially at continental scale Flux variations are predominantly controlled by El Nino events, with the exception of the post-Pinatubo period of the early 1990s Differences between the two land models result mainly from the response of heterotrophic respiration to precipitation and temperature The “Lloyd and Taylor” formulation of LPJ [Lloyd and Taylor, 1994] agrees better with the inverse estimates Over the ocean, inversion and model results agree only in the equatorial Pacific and partly in the austral ocean In the austral ocean, an increased CO2 sink is present in the inversion and OPA model, and results from increased stratification of the ocean In the northern oceans, the inversions estimate large flux variations in line with time-series observations of the subtropical Atlantic, but not supported by the two model estimates, thus suggesting that the CO2 variability from high-latitude oceans needs further investigation

The COVID-19 lockdowns: a window into the Earth System

Abstract: Restrictions to reduce human interaction have helped to avoid greater suffering and death from the COVID-19 pandemic, but have also created socioeconomic hardship. This disruption is unprecedented in the modern era of global observing networks, pervasive sensing and large-scale tracking of human mobility and behaviour, creating a unique test bed for understanding the Earth System. In this Perspective, we hypothesize the immediate and long-term Earth System responses to COVID-19 along two multidisciplinary cascades: energy, emissions, climate and air quality; and poverty, globalization, food and biodiversity. While short-term impacts are dominated by direct effects arising from reduced human activity, longer-lasting impacts are likely to result from cascading effects of the economic recession on global poverty, green investment and human behaviour. These impacts offer the opportunity for novel insight, particularly with the careful deployment of targeted data collection, coordinated model experiments and solution-oriented randomized controlled trials, during and after the pandemic. The COVID-19 pandemic has caused substantial global impact. This Perspective provides insight into the environmental effects of the pandemic, documenting how it offers an opportunity to better understand the Earth System.

The Ensemble Kalman Filter: Theoretical formulation and practical implementation

Abstract: The purpose of this paper is to provide a comprehensive presentation and interpretation of the Ensemble Kalman Filter (EnKF) and its numerical implementation. The EnKF has a large user group, and numerous publications have discussed applications and theoretical aspects of it. This paper reviews the important results from these studies and also presents new ideas and alternative interpretations which further explain the success of the EnKF. In addition to providing the theoretical framework needed for using the EnKF, there is also a focus on the algorithmic formulation and optimal numerical implementation. A program listing is given for some of the key subroutines. The paper also touches upon specific issues such as the use of nonlinear measurements, in situ profiles of temperature and salinity, and data which are available with high frequency in time. An ensemble based optimal interpolation (EnOI) scheme is presented as a cost-effective approach which may serve as an alternative to the EnKF in some applications. A fairly extensive discussion is devoted to the use of time correlated model errors and the estimation of model bias.

Carbon and Other Biogeochemical Cycles

Abstract: For base year 2010, anthropogenic activities created ~210 (190 to 230) TgN of reactive nitrogen Nr from N2. This human-caused creation of reactive nitrogen in 2010 is at least 2 times larger than the rate of natural terrestrial creation of ~58 TgN (50 to 100 TgN yr−1) (Table 6.9, Section 1a). Note that the estimate of natural terrestrial biological fixation (58 TgN yr−1) is lower than former estimates (100 TgN yr−1, Galloway et al., 2004), but the ranges overlap, 50 to 100 TgN yr−1 vs. 90 to 120 TgN yr−1, respectively). Of this created reactive nitrogen, NOx and NH3 emissions from anthropogenic sources are about fourfold greater than natural emissions (Table 6.9, Section 1b). A greater portion of the NH3 emissions is deposited to the continents rather than to the oceans, relative to the deposition of NOy, due to the longer atmospheric residence time of the latter. These deposition estimates are lower limits, as they do not include organic nitrogen species. New model and measurement information (Kanakidou et al., 2012) suggests that incomplete inclusion of emissions and atmospheric chemistry of reduced and oxidized organic nitrogen components in current models may lead to systematic underestimates of total global reactive nitrogen deposition by up to 35% (Table 6.9, Section 1c). Discharge of reactive nitrogen to the coastal oceans is ~45 TgN yr−1 (Table 6.9, Section 1d). Denitrification converts Nr back to atmospheric N2. The current estimate for the production of atmospheric N2 is 110 TgN yr−1 (Bouwman et al., 2013).

Trends in the sources and sinks of carbon dioxide

Abstract: Efforts to control climate change require the stabilization of atmospheric CO2 concentrations. This can only be achieved through a drastic reduction of global CO2 emissions. Yet fossil fuel emissions increased by 29% between 2000 and 2008, in conjunction with increased contributions from emerging economies, from the production and international trade of goods and services, and from the use of coal as a fuel source. In contrast, emissions from land-use changes were nearly constant. Between 1959 and 2008, 43% of each year's CO2 emissions remained in the atmosphere on average; the rest was absorbed by carbon sinks on land and in the oceans. In the past 50 years, the fraction of CO2 emissions that remains in the atmosphere each year has likely increased, from about 40% to 45%, and models suggest that this trend was caused by a decrease in the uptake of CO2 by the carbon sinks in response to climate change and variability. Changes in the CO2 sinks are highly uncertain, but they could have a significant influence on future atmospheric CO2 levels. It is therefore crucial to reduce the uncertainties.