On the potential role of marine calcifiers in glacial‐interglacial dynamics

Abstract

[1] Ice core measurements have revealed a highly asymmetric cycle in Antarctic temperature and atmospheric CO 2 over the last 800 kyr. Both CO 2 and temperature decrease over 100 kyr going into a glacial period and then rise steeply over less than 10 kyr at the end of a glacial period. There does not yet exist wide agreement about the causes of this cycle or about the origin of its shape. Here we explore the possibility that an ecologically driven oscillator plays a role in the dynamics. A conceptual model describing the interaction between calcifying plankton and ocean alkalinity shows interesting features: (i) It generates an oscillation in atmospheric CO 2 with the characteristic asymmetric shape observed in the ice core record, (ii) the system can transform a sinusoidal Milankovitch forcing into a sawtooth-shaped output, and (iii) there are spikes of enhanced calcifier productivity at the glacial-interglacial transitions, consistent with several sedimentary records. This suggests that ecological processes might play an active role in the observed glacial-interglacial cycles.

Carbon burial in deep-sea sediment and implications for oceanic inventories of carbon and alkalinity over the last glacial cycle

“…10 Several mechanisms that have been proposed to explain low glacial atmospheric CO 2 concentrations involve decreased CaCO 3 burial (Vecsei and Berger, 2004;Hain et al, 2014a), which would have raised ALK and thereby increased CO 2 solubility. One of these calls on changes in ocean circulation (Boyle, 1988;Jaccard et al, 2009) or biological production (Archer et al, 2000;Omta et al, 2013) to have raised the DIC in the deep ocean and therefore have lowered deep ocean CO 3 2-, requiring the ocean to compensate by dissolving CaCO 3 until the alkalinity was raised sufficiently to restore CO 3 2-…”

Inherent characteristics of sawtooth cycles can explain different glacial periodicities

“…As in Omta et al (2013), we therefore apply a periodic forcing to the reaction rate parameter k which directly impacts the calcifier population growth rate:…”

“…We use the calcifier-alkalinity model that has been described and discussed in detail in Omta et al (2013); the model code, including brief instructions, has been attached as online Auxiliary Material. In its simplest version, the model consists of two differential equations for ocean alkalinity A and a calcifier population C (variables and parameter values listed in Table 1): Alkalinity A is added to the ocean at a fixed rate I through river runoff resulting from weathering and consumed by a population of calcifiers C, growing at an effective rate kA and sedimenting at a rate M. The autocatalytic process described in the set of Eq.…”

“…Rather, we argue that such changes are an inherent feature of sawtooth-spike oscillations, which the glacial-interglacial cycles resemble. We use the previously developed calcifier-alkalinity model (Omta et al 2013) as an illustrative example of a system exhibiting sawtooth-spike behavior. Within the context of this model, the rapid deglaciations and the different glacial periodicities need to be related to atmospheric CO 2 .…”

“…In Omta et al (2013), simulations were performed with the most idealized version of the calcifier-alkalinity model under a 20-kyr sinusoidal forcing with relative amplitude α = 0.0025 (that is, variations in the parameter k were a factor 0.0025, or 0.25 % around the mean). The system exhibited cycles with the same periodicity as the forcing.…”