Ice Core Records of Atmospheric N 2 O Covering the Last 106,000 Years (original) (raw)
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Isotopic constraints on marine and terrestrial N2O emissions during the last deglaciation
Nature, 2014
Nitrous oxide (N2O) is an important greenhouse gas and ozone-depleting substance that has anthropogenic as well as natural marine and terrestrial sources. The tropospheric N2O concentrations have varied substantially in the past in concert with changing climate on glacial-interglacial and millennial timescales. It is not well understood, however, how N2O emissions from marine and terrestrial sources change in response to varying environmental conditions. The distinct isotopic compositions of marine and terrestrial N2O sources can help disentangle the relative changes in marine and terrestrial N2O emissions during past climate variations. Here we present N2O concentration and isotopic data for the last deglaciation, from 16,000 to 10,000 years before present, retrieved from air bubbles trapped in polar ice at Taylor Glacier, Antarctica. With the help of our data and a box model of the N2O cycle, we find a 30 per cent increase in total N2O emissions from the late glacial to the interg...
Biogeosciences
interactions regulate N availability for plant growth and for emissions of nitrous oxide (N 2 O) and the uptake of carbon dioxide. Future projections of these terrestrial greenhouse gas fluxes are strikingly divergent, leading to major uncertainties in projected global warming. Here we analyse the large increase in terrestrial N 2 O emissions over the past 21 000 years as reconstructed from ice-core isotopic data and presented in part 1 of this study. Remarkably, the increase occurred in two steps, each realized over decades and within a maximum of 2 centuries, at the onsets of the major deglacial Northern Hemisphere warming events. The data suggest a highly dynamic and responsive global N cycle. The increase may be explained by an increase in the flux of reactive N entering and leaving ecosystems or by an increase in N 2 O yield per unit N converted. We applied the LPX-Bern dynamic global vegetation model in deglacial simulations forced with Earth system model climate data to investigate N 2 O emission patterns, mechanisms, and C-N coupling. The N 2 O emission changes are mainly attributed to changes in temperature and precipitation and the loss of land due to sea-level rise. LPX-Bern simulates a deglacial increase in N 2 O emissions but underestimates the reconstructed increase by 47 %. Assuming timeindependent N sources in the model to mimic progressive N limitation of plant growth results in a decrease in N 2 O emissions in contrast to the reconstruction. Our results appear consistent with suggestions of (a) biological controls on ecosystem N acquisition and (b) flexibility in the coupling of the C and N cycles during periods of rapid environmental change. A dominant uncertainty in the explanation of the reconstructed N 2 O emissions is the poorly known N 2 O yield per N lost through gaseous pathways and its sensitivity to soil conditions. The deglacial N 2 O record provides a constraint for future studies.
Atmospheric Nitrous Oxide Variations on Centennial Time Scales During the Past Two Millennia
Global Biogeochemical Cycles, 2020
The continuous growth of atmospheric nitrous oxide (N 2 O) is of concern for its potential role in global warming and future stratospheric ozone destruction. Climate feedbacks that enhance N 2 O emissions in response to global warming are not well understood, and past records of N 2 O from ice cores are not sufficiently well resolved to examine the underlying climate-N 2 O feedbacks on societally relevant time scales. Here, we present a new high-resolution and high-precision N 2 O reconstruction obtained from the Greenland NEEM (North Greenland Eemian Ice Drilling) and the Antarctic Styx Glacier ice cores. Covering the N 2 O history of the past two millennia, our reconstruction shows a centennial-scale variability of~10 ppb. A pronounced minimum at~600 CE coincides with the reorganizations of tropical hydroclimate and ocean productivity changes. Comparisons with proxy records suggest association of centennial-to millennial-scale variations in N 2 O with changes in tropical and subtropical land hydrology and marine productivity. Plain Language Summary Nitrous oxide (N 2 O) is a greenhouse and ozone-depleting gas. The growing level of N 2 O in the atmosphere is of global concern, and records of past N 2 O variations can provide an important context for understanding the links between N 2 O and climate change. In this study, we report new, high-quality N 2 O records covering the last two millennia using ice cores obtained from Greenland and Antarctica. Our N 2 O records show rapid centennial-scale changes in atmospheric N 2 O and confirm a pronounced minimum near 600 CE. Comparison with climate records suggests that hydroclimate change on land and changes in marine productivity contribute to centennial-to millennial-scale N 2 O variations.
High-resolution Holocene N2O ice core record and its relationship with CH4and CO2
Global Biogeochemical Cycles, 2002
Nitrous oxide (N 2 O) concentration records exist for the last 1000 years and for time periods of rapid climatic changes like the transition from the last glacial to today's interglacial and for one of the fast climate variations during the last ice age. Little is known, however, about possible N 2 O variations during the more stable climate of the present interglacial (Holocene) spanning the last 11 thousand years. Here we fill this gap with a high-resolution N 2 O record measured along the European Project for Ice Coring in Antarctica (EPICA) Dome C Antarctic ice core. On the same ice we obtained high-resolution methane and carbon dioxide records. This provides the unique opportunity to compare variations of the three most important greenhouse gases (after water vapor) without any uncertainty in their relative timing. The CO 2 and CH 4 records are in good agreement with previous measurements on other ice cores. The N 2 O concentration started to decrease in the early Holocene and reached minimum values around 8 ka (<260 ppbv) before a slow increase to its preindustrial concentration of $265 ppbv.
Changes in global nitrogen cycling during the Holocene epoch
Nature, 2013
Human activities have doubled the pre-industrial supply of reactive nitrogen on Earth, and future rates of increase are expected to accelerate. Yet little is known about the capacity of the biosphere to buffer increased nitrogen influx. Past changes in global ecosystems following deglaciation at the end of the Pleistocene epoch provide an opportunity to understand better how nitrogen cycling in the terrestrial biosphere responded to changes in carbon cycling. We analysed published records of stable nitrogen isotopic values (δ(15)N) in sediments from 86 lakes on six continents. Here we show that the value of sedimentary δ(15)N declined from 15,000 years before present to 7,056 ± 597 years before present, a period of increasing atmospheric carbon dioxide concentrations and terrestrial carbon accumulation. Comparison of the nitrogen isotope record with concomitant carbon accumulation on land and nitrous oxide in the atmosphere suggests millennia of declining nitrogen availability in terrestrial ecosystems during the Pleistocene-Holocene transition around 11,000 years before present. In contrast, we do not observe a consistent change in global sedimentary δ(15)N values during the past 500 years, despite the potential effects of changing temperature and nitrogen influx from anthropogenic sources. We propose that the lack of a single response may indicate that modern increases in atmospheric carbon dioxide and net carbon sequestration in the biosphere have the potential to offset recent increased supplies of reactive nitrogen in some ecosystems.
Isotopic constraints on glacial/interglacial changes in the oceanic nitrogen budget
2004
1] We investigate the response of the 15 N/ 14 N of oceanic nitrate to glacial/interglacial changes in the N budget, using a geochemical box model of the oceanic N cycle that includes N 2 fixation and denitrification in the sediments and suboxic water column. This model allows us to quantify the isotopic response of different oceanic nitrate pools to deglacial increases in water column and sedimentary denitrification, given a range of possible feedbacks between nitrate concentration and N 2 fixation/denitrification. This response is compared to the available paleoceanographic data, which suggest an early deglacial maximum in nitrate 15 N/ 14 N in suboxic zones and no significant glacialto-late Holocene change in global ocean nitrate 15 N/ 14 N. Consistent with the work of Brandes and Devol [2002], we find that the steady state 15 N/ 14 N of oceanic nitrate is controlled primarily by the fraction of total denitrification that occurs in the water column. Therefore a deglacial peak in the ratio of water column-to-sediment denitrification, caused by either a strong feedback between water column denitrification and the N reservoir or by an increase in sediment denitrification due to sea level rise, can explain the observed deglacial 15 N/ 14 N maximum in sediments underlying water column denitrification zones. The total denitrification rate and the mean ocean nitrate concentration are also important determinants of steady state nitrate 15 N/ 14 N. For this reason, modeling a realistic deglacial 15 N/ 14 N maximum further requires that the combined negative feedbacks from N 2 fixation and denitrification are relatively strong, and N losses are relatively small. Our results suggest that the glacial oceanic N inventory was at most 30% greater than today's and probably less than 10% greater.
Glacial/interglacial variations in atmospheric carbon dioxide
Nature, 2000
Twenty years ago, measurements on ice cores showed that the concentration of carbon dioxide in the atmosphere was lower during ice ages than it is today. As yet, there is no broadly accepted explanation for this difference. Current investigations focus on the ocean's 'biological pump', the sequestration of carbon in the ocean interior by the rain of organic carbon out of the surface ocean, and its effect on the burial of calcium carbonate in marine sediments. Some researchers surmise that the whole-ocean reservoir of algal nutrients was larger during glacial times, strengthening the biological pump at low latitudes, where these nutrients are currently limiting. Others propose that the biological pump was more efficient during glacial times because of more complete utilization of nutrients at high latitudes, where much of the nutrient supply currently goes unused. We present a version of the latter hypothesis that focuses on the open ocean surrounding Antarctica, involvin...