{'fraction_non_alphanumeric': 0.02738283307003686, 'fraction_numerical': 0.02764612954186414, 'mean_word_length': 5.03015873015873, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Structure of the late Palaeocene carbon isotope excursion

The gradual warming trend that began in the late Palaeocene and persisted into the early Eocene was punctuated by a brief episode of greenhouse gas induced global warming termed the late Palaeocene thermal maximum (LPTM; Zachos et al. 1993). Accompanying the onset of the LPTM was a dramatic benthic foraminifer extinction (as reviewed in Thomas & Shackleton 1996), increased turnover and morphologic change of surface marine and terrestrial species (Lu & Keller 1993; Kelly et al. 1996; Gingerich 1989; Maas et al. 1995), and an anomalous negative shift in the global carbon isotope (δC) record (Kennett & Stott 1991; Koch et al. 1992). The dissociation of the isotopically light greenhouse gas methane (CH4) from sub-marine gas hydrate accumulations has been proposed to explain both the amplitude of the δC excursion, and the abrupt jump in temperatures (Dickens et al. 1995). Gas hydrates are kept in a solid state by the combination of low temperature and high pressure, therefore an inferred switch to a halo-thermal ocean circulation system has been suggested as the triggering mechanism for CH4 release at the onset of the LPTM (Dickens et al. 1995; Bralower et al. 1997). In this scenario, sinking waters from the low latitudes may have warmed intermediate to deep waters, causing thermal instability and liberation of trapped CH4 at these depths. In order to investigate the global changes that occurred around this extreme climate we produced an ultra-high resolution oxygen and carbon isotope record from sediments recovered by the Ocean Drilling Program (ODP). We analysed bulk carbonates from Holes 690B, 865C, and 1051B and compared our data with existing high-resolution data from Site 1001 (Bralower et al. 1997). Our findings from Holes 690B and 1051B indicate that both δO and δC LPTM excursions are more complex than previously thought (Fig. 1). The records indicate that the δC anomaly is preceded by a brief period of sea surface temperature (SST) cooling in the high latitude Weddell Sea (Site 690), and no significant SST change in the western North Atlantic (Site 1051) at the time of inferred reversal to halo-thermal circulation (C, Fig. 1). Following the benthic foraminifer extinction both δC and δO records from Holes 690B and 1051B display a rapid, and stepped, fall to minimum values (Bains et al. 1999). The recovery to pre-excursion values is more gradual and does not contain complex structure. There is no evidence from our records to suggest that oceanic temperatures were increasing monotonously before the excursion, which suggests that passing a threshold temperature, causing a reorganisation of oceanic deep-water circulation, might not have been the cause of the events, recorded across this interval. The complex nature of the δC and δO negative isotope shifts and the presence of plateaus in the records imply brief periods of stasis in the global carbon cycle between sequential outgassing episodes. We propose that the late Palaeocene δC and δO anomalies represent multiple injections of light carbon into the ocean and atmosphere as geographically diverse hydrate reservoirs became unstable at slightly different times. This could reflect a difference in the timing of deep water warming at different latitudes, depths, and geographic locations. Magnetobiostratigraphic correlations are not useful for timing and characterising the global or regional nature of events surrounding the LPTM because it falls within the long magnetic reversal, Chron C24r (Berggren et al. 1995). Calcareous microfossils, such as foraminifers, which serve as zonal markers are often absent (especially in high latitude Sites such as 690; Kennett & Stott 1991) and are frequently affected by dissolution (Aubry et