Pollen and macrofossil‐inferred palaeoclimate at the Ridge Site, Hudson Bay Lowlands, Canada: evidence for a dry climate and significant recession of the Laurentide Ice Sheet during Marine Isotope Stage 3

Abstract

We examine pollen, macrofossils and sedimentological proxies from the Ridge Site, an 18‐m sequence of glacial and non‐glacial sediments exposed along the bank of the Ridge River in the southern Hudson Bay Lowlands (HBL), Canada. As the HBL is located in the previously glaciated region of North America, palaeorecords from this region have important implications for understanding ice‐sheet palaeogeography and climate for the late Pleistocene. Two diamicton units were interpreted as subglacial till deposited by a glacier flowing toward the south‐southwest (lower diamicton) and west‐southwest (upper diamicton), respectively. Confined between these tills is a 6‐m non‐glacial unit, constrained to Marine Isotope Stage 3 (MIS 3; c. 57 000 to c. 29 000 a BP) by three radiocarbon dates. Quantitative analyses of the pollen record (dominated by Sphagnum, Cyperaceae, Pinus, Picea, Salix, Alnus and Betula) suggest that average summer temperature (June, July, August) was 14.6±1.51 °C, which is similar to that of the present day at the site. Total annual precipitation was 527±170 mm as compared to 705 mm present‐day. The macrofossil record confirmed the local presence of Betula, Salix and conifers. Our results, in combination with other records from the periphery of the Laurentide Ice Sheet, suggest that vast boreal forest‐type vegetation, along with a drier interstadial climate, existed in the region during MIS 3. We also compare pollen‐derived palaeoclimate reconstructions from the Ridge Site with reconstructions from a previously published site along the Nottaway River, HBL, which was dated to MIS 5a–d (c. 109 000 to c. 82 000 a BP). This comparison suggests that, with additional data, it may be possible to differentiate MIS 3 and MIS 5 deposits in the HBL on the basis of relative continentality, with MIS 3 characterized by lower total annual precipitation, and MIS 5 by values similar or greater than present‐day.

Middle Wisconsinan marine shells near Repulse Bay, Nunavut, Canada: implications for Marine Isotope Stage 3 ice‐free conditions and Laurentide Ice Sheet dynamics in north‐west Hudson Bay

“…This scenario requires deglaciation of at least the northern part of Hudson Bay, and perhaps areas farther south (although not necessary), which in that case sustains the interpretation of ice-free conditions during parts of MIS 3 in the HBL (e.g. Dalton et al, 2016Dalton et al, , 2017. This configuration also supports MIS 3 radiocarbon dates along Hudson Strait/ Foxe Peninsula (Laymon, 1991;Manley, 1996;Utting et al, 2016) and upholds hypothesis III of Dredge and Campbell et al, 2013).…”

“…This scenario requires deglaciation of at least the northern part of Hudson Bay, and perhaps areas farther south (although not necessary), which in that case sustains the interpretation of ice‐free conditions during parts of MIS 3 in the HBL (e.g. Dalton et al , , ). This configuration also supports MIS 3 radiocarbon dates along Hudson Strait/Foxe Peninsula (Laymon, ; Manley, ; Utting et al , ) and upholds hypothesis III of Dredge and Thorleifson () that shows a calving bay penetrating into the heart of the ice sheet induced by a marine‐based instable ice‐mass during relatively high glacio‐isostatic and eustatic seas.…”

“…Dredge and Thorleifson, , and references herein; Berger and Nielsen, ; Thorleifson et al , ) and is still disputed today based on recent work. Using U–Th dating of fossil wood in the HBL, Allard et al () refuted ice‐free conditions in Hudson Bay during MIS 3 while Dalton et al (, ), using mainly radiocarbon dates of the Missinaibi Formation in the HBL, suggested a possible ice‐free HBL during parts of MIS 3. The HBL lie at the center of the LIS so the presence of sea water in Hudson Bay is a marker for a major reduction in glacial ice extent.…”

“…Conflicting evidence for the extent of glacial ice cover and marine incursion in the Hudson Bay Lowlands (HBL) during MIS 3 (e.g. Allard et al , ; Dalton et al , , ) emphasizes the need for increased and well‐dated terrestrial paleorecords to reconstruct the growth and decay of paleoice sheets.…”

A new global ice sheet reconstruction for the past 80 000 years

“…Recent work in the Hudson Bay region in North America 5 – 7 shows that during part of MIS 3, ice-free conditions may have existed. Under this interpretation, the climatic conditions in this area were favorable to allow the growth of forests, with a climate that was potentially analogous to present 8 . This would indicate that not only was the Laurentide Ice Sheet reduced in size but it also had to be far enough removed from southern Hudson Bay to not strongly affect the climate there.…”