Glacial‐interglacial variability in denitrification in the World's Oceans: Causes and consequences

Abstract

Abstract. The late Quaternary history of water-column denitrifcation of the eastern Pacific margins and the Arabian Sea is reconstructed using sedimentary •515N measurements. The •515N values in six piston cores raised from these regions show remarkably similar cyclic variations, being heavy (9-10.5%o) during the interglacials and 2-3%0 lighter during the glacials. This implies that denitrification in these regions decreased substantially during the glacial periods. The glacial decline in denitrification is attributed to reduce• upwelling and flux of organic material through the oxygen minimum zone. Since water-column denitrification in these areas accounts for about half of the fixed-nitrogen loss in the modem ocean, the inferred decrease in denitrification should have increased the oceanic nitrate inventory during glacial periods. Because nitrate is a limiting nutrient, oceanic productivity and attendant changes in CO2 may therefore have been modulated on glacial-interglacial timescales by variations in the oceanic NO3-content.

North Pacific-wide spreading of isotopically heavy nitrogen during the last deglaciation: Evidence from the western Pacific

“…The two major δ 15 N peaks occurred during two warm periods: Bølling/Allerød and the period after Younger Dryas during transgression (Fig. 3b) resembling the trends observed not only in the ENP but also in the Arabian Sea (Ganeshram et al, 1995(Ganeshram et al, , 2000Deutsch et al, 2004 and references therein).…”

“…Kao (sjkao@gate.sinica.edu.tw) Thus, there is a growing interest in the interaction between climate and N biogeochemistry. Evidence for strong links between climate and key N cycling processes -N 2 fixation and denitrification -has been accumulating (Altabet et al, 1995;Ganeshram et al, 1995;Falkowski, 1997), and several researchers have hypothesized indirect influences of the marine fixed N inventory on paleo-climate (McElroy, 1983;Ganeshram et al, 1995Ganeshram et al, , 2000Pedersen and Bertrand, 2000;Suthhof et al, 2001;Altabet et al, 2002). However, considerable uncertainty still remains regarding changes in global ocean nitrate inventory, particularly during the last glacial period (Deutsch et al, 2004;Altabet, 2007).…”

Glacial‐interglacial modulation of eastern tropical North Pacific denitrification over the last 1.8‐Myr

“…At present, water column denitrification accounts for up to the half of the total oceanic nitrogen loss [Codispoti et al, 2001]. During late Pleistocene glacial periods, denitrification in the oxygen minimum zones (OMZs) of the world's ocean was significantly reduced or even absent [Altabet et al, 1999a;Ganeshram et al, 2000;Kienast et al, 2002]. Reduced denitrification could increase the oceanic nitrate inventory, increase the strength of ocean carbon pump, and thus could potentially draw down atmospheric CO 2 during glacial periods [Altabet et al, 2002;Ganeshram et al, 2000].…”

Constraints on oceanic N balance/imbalance from sedimentary <sup>15</sup>N records

“…It is likely the only means to address the question of N cycle balance both over its most recent residence time period as well as more distant past. The more successful applications have been reconstructions of past variation in regional processes such as water column denitrification (Ganeshram et al, 1995;Pride et al, 1999;Ganeshram et al, 2000;Altabet et al, 2002;Thunell and Kepple, 2004) and near-surface NO − 3 drawdown (Francois et al, 1997;Sigman et al, 1999). Attempts have been made to reconstruct the average δ 15 N of marine N and a number of theoretical studies point to this parameter as reflecting the balance between the largest N flux terms (Brandes and Devol, 2002).…”