A new Shoreline displacement model for the last 7 ka from eastern James Bay, Canada

Abstract

The shoreline displacement history of the eastern James Bay lowlands in the last 7 ka has been investigated by means of AMS radiocarbon dating of sediments cored from wetlands. We present twelve radiocarbon dates on macrofossils from six sites spread along a gradient of increasing land age and elevation. Palynomorph analysis (pollen, spores, and dinoflagellate cysts) was used to define the isolation stratigraphy. During the last 7 ka the shoreline elevation has regressed at a decreasing rate. The rate of shoreline emergence was initially rapid (6. 5 m/ 100 yr) between 6850 and 6400 cal yr BP then slowed down to 1.4– 2 m/ 100 yr during the late Holocene. Examination of previous relative sea level data based upon mollusc shells reveals high levels of uncertainty that mask potential temporal variability.

A high-resolution record of carbon accumulation rates during boreal peatland initiation

“…This figure represents the maximum area of peatland that may have originated from tidal wetlands in Canada, alone. Indeed, some of these wetlands could have originated in lake basins, such as kettle basins, but studies show that large blanket areas of peatlands such as those occupying the Hudson Bay Lowlands developed from tidal marshes which followed the marine water retreat (Glaser et al, 2004;Pendea et al, 2010). Although more work is needed, we suggest that the high carbon sequestration capacity of the early postglacial fens that succeeded tidal wetlands after the shoreline retreat may explain, in part, the early Holocene reduction in atmospheric CO 2 .…”

“…The marine transgression was brief and followed by shoreline regression under the influence of glacio-isostatic rebound. Over the last ∼ 7000 yr, landscape emergence has been underway at a rate ranging from 6.5 m / 100 yr between 7000 and 6500 cal yr BP to 1.4-2 m / 100 yr during the late Holocene (Pendea et al, 2010).…”

“…This increased C storage has been attributed to climate change and increased productivity (MacDonald et al, 2006;Yu et al, 2011). However, this period also would have corresponded to early stages of peatland development following retreat of ice sheets and substantial increases in storage could be associated with wetland evolution via lake filling (e.g., Kubiw et al, 1989) or following marine shoreline emergence (e.g., Shennan et al, 1999Shennan et al, , 2000Pendea et al, 2010). Some northern peatlands originated as marine shorelines emerged from the sea, isostatically recovering from crustal depression caused by ice sheets (e.g., Shennan et al, 2000;Pendea et al, 2010).…”

“…However, this period also would have corresponded to early stages of peatland development following retreat of ice sheets and substantial increases in storage could be associated with wetland evolution via lake filling (e.g., Kubiw et al, 1989) or following marine shoreline emergence (e.g., Shennan et al, 1999Shennan et al, , 2000Pendea et al, 2010). Some northern peatlands originated as marine shorelines emerged from the sea, isostatically recovering from crustal depression caused by ice sheets (e.g., Shennan et al, 2000;Pendea et al, 2010). Immediately after emergence, tidal marsh deposits formed and, with continued crustal uplift, marshes were isolated from tidal influence and transformed into freshwater minerotrophic fens.…”

Long-term dynamics of a palsa in the sporadic permafrost zone of northwestern Quebec (Canada)

“…According to the relative sea level curve of the eastern James Bay area recently updated by Pendea et al (2010), the study site, located at an altitude of 163 m asl, would have emerged from the Tyrrell Sea waters around 6100 cal years BP. The radiocarbon date obtained at the gyttja-peat transition (162 cm) indicates that peat began to accumulate around 5310 cal years BP.…”