Calcium and iron of ODP Hole 113-690B

We have developed a new orbital chronology for Ocean Drilling Program (ODP) Site 690 (Weddell Sea, Southern Ocean) by using spectral analysis of high-resolution geochemical records. The LPTM interval spans 11 precessional cycles yielding a duration of 210 to 220 k.y.

The delta13C anomaly associated with the LPTM has a magnitude of about -2.5 per mil to -3 per mil; we show that about -2 per mil of the excursion occurs within two steps that each were less than 1000 yr in duration. The remainder developed through a series of steps over ~52 k.y. The timing of these steps is consistent with a series of nearly catastrophic releases of methane from gas hydrates, punctuated by intervals of relative equilibria between hydrate dissociation and carbon burial.