A 1000-year high precision record of δ¹³C in atmospheric CO₂

Abstract

We present measurements of the stable carbon isotope ratio in air extracted from Antarctic ice core and firn samples. The same samples were previously used by Etheridge and co-workers to construct a high precision 1000-year record of atmospheric CO 2 concentration, featuring a close link between the ice and modern records and high-time resolution. Here, we start by confirming the trend in the Cape Grim in situ d13C record from 1982 to 1996, and extend it back to 1978 using the Cape Grim Air Archive. The firn air d13C agrees with the Cape Grim record, but only after correction for gravitational separation at depth, for diffusion effects associated with disequilibrium between the atmosphere and firm, and allowance for a latidudinal gradient in d13C between Cape Grim and the Antarctic coast. Complex calibration strategies are required to cope with several additional systematic influences on the ice core d13C record. Errors are assigned to each ice core value to reflect statistical and systematic biases (between ±0.025‰ and ±0.07‰); uncertainties (of up to ±0.05‰) between core-versus-core, ice-versus-firn and firn-versus-troposphere are described separately. An almost continuous atmospheric history of d13C over 1000 years results, exhibiting significant decadal-to-century scale variability unlike that from earlier proxy records. The decrease in d13C from 1860 to 1960 involves a series of steps confirming enhanced sensitivity of d13C to decadal timescale-forcing, compared to the CO 2 record. Synchronous with a ''Little Ice Age'' CO 2 decrease, an enhancement of d13C implies a terrestrial response to cooler temperatures. Between 1200 AD and 1600 AD, the atmospheric d13C appear stable.

A revised 1000 year atmospheric δ13C‐CO2 record from Law Dome and South Pole, Antarctica

“…[98] The main features of the previously published CO 2 and ı 13 C records Francey et al, 1999;MacFarling Meure et al, 2006] remain essentially unchanged. However, the higher sample density in the twentieth century provides more certainty on the data (Figure 6).…”

“…They feature a space, between the internal grater and the external container where chips produced by the grating action fall to avoid clogging the grater. Grater 1, also used in earlier studies Francey et al, 1999;MacFarling Meure et al, 2006], consists of a single cylindrical container sealed with two end caps by means of indium wire. The ice grater is welded to one end cap.…”

Presentation, calibration and validation of the low-order, DCESS Earth System Model (Version 1)

“…We adjusted the four free parameters of this module (Table 1) to give a global mean atmospheric temperature of 15 • C and a climate sensitivity of 3 • C per doubling of atmospheric pCO 2 and poleward heat and water vapor transports in the atmosphere across the sector boundary consistent with observations (Trenberth and Caron, 2001;Dai and Trenberth, 2002). In the second calibration step, we considered the ocean and land biosphere modules coupled to the preliminarilycalibrated, atmosphere module, with pre-industrial atmospheric δ 13 C of −6.4‰, observed atmospheric pO 2 of 0.2095 atm and observed ocean mean PO 4 , DIC and ALK of 2.12×10 −3 , 2.32 and 2.44 mol m −3 (Francey, 1999;Keeling et al, 1998;Shaffer, 1993Shaffer, , 1996. Atmospheric 14 C production was adjusted to maintain atmospheric 14 C at 0‰.…”

“…Values before 1860 were set to the 1860 value and values after 1992 were set to the 1992 value. Atmospheric δ 13 C observations were taken from Francey et al (1999) and atmospheric 14 C observations were taken from Stuiver and Quay (1981). The fossil fuel -O 2 :C mole ratio was taken to be 1.391 in the pO 2 simulation (Keeling et al, 1998). of total ocean DIC increase is found in this sector with only 13.4% of the model ocean volume.…”

Regional And Watershed-Scale Coherence In the Stable-Oxygen and Carbon Isotope Ratio Time Series In Tree Rings Of Coast Redwood (Sequoia sempervirens)

“…Maximum interannual variation in d 13 C was between 1 and 3% for both latewood and middlewood segments at each site (Figure 3; data not shown for other sites). Many d 13 C time series produced lowerfrequency trends ( Figure 3B) that were likely associated with changing concentration and d 13 C values of atmospheric CO 2 (Francey et al 1999;McCarroll et al 2009). To correct for this we calculated D 13 C values for all time series: D 13 C 5 (d 13 C source 2 d 13 C product )/(1 + d 13 C product ), where source is atmospheric CO 2 and product in this case is cellulose (Farquhar et al 1982).…”