Stratigraphy, pollen and ¹⁴C dating of Johnston's Gum Hole, a late Quaternary fossil kauri (Agathis australis) site, Northland, New Zealand

Abstract

Johnston's Gum Hole provides a discontinuous pollen record commencing late in Marine Isotope Stage 5 (MIS 5). In combination with other published records from the region, the Aupouri Peninsula is reconstructed to have been continuously forested through much of the last glacial cycle with the oscillation of Agathis-and Nothofagus-dominated forest corresponding to stadials and interstadials, respectively. A northward latitudinal expansion of beech forest to 358 S is demonstrated. Kauri demise at the close of MIS 5 appears to have been due to flooding of the site. The elimination of kauri in MIS 3 was also associated with rewetting of the substrate, but could have been a more catastrophic event. The presence of both MIS 5 and MIS 3 kauri wood at the site suggests that other Aupouri peat swamps may also preserve timber of these ages, and demonstrate the potential of this area for providing MIS 3 and MIS 5 tree ring records.

Examining plant physiological responses to climate change through an evolutionary lens

“…in our study, glacial Agathis spp. experienced warmer and wetter conditions during the last glacial period compared with modern climates (Elliot et al, 2005;Horrocks et al, 2007;D'Costa et al, 2008). We examined the effects of increasing [CO 2 ] in controlled locations in both study systems; the full Juniperus spp.…”

An MIS 5a/b to MIS 3 bog sequence from Henderson Bay, northern New Zealand

“…This event must be younger than the underlying peats, the minimum age of which is indicated by a radiocarbon age of !50 14 C ka BP (Wk 18540) obtained from an in situ tree stump in palaeosol P1 (Fig. 3) A recent re-evaluation of previously finite ages of wood from Aupouri Peninsula (Hogg et al 2006(Hogg et al , 2007 has shown that much of the wood preserved on Aupouri Peninsula is actually of 'infinite' radiocarbon age and much of the timber is likely to be of Last Interglacial affinity (D'Costa et al 2008). While our radiocarbon age must be regarded as a minimum, the pollen record can be used to refine the age of our sequence by comparison with other Northland pollen records (e.g.…”

“…While our radiocarbon age must be regarded as a minimum, the pollen record can be used to refine the age of our sequence by comparison with other Northland pollen records (e.g. Newnham et al 2004;D'Costa et al 2008).…”

“…5). The only other long Last Glacial cycle records from Northland are (1) the discontinuous Lake Omapere record which covers c. 80 ka with sedimentation inferred as commencing towards the end of MIS 5a (Newnham et al 2004) and (2) the discontinuous mid Last Glacial cycle (c. MIS 3 to 5a) pollen record from Johnston's Gum Hole (D'Costa et al 2008). At Lake Omapere, the lower parts of the cores ascribed to MIS 5a and 4 contain percentages of Fuscospora pollen similar to those observed on either side of the HB2/1 boundary at Henderson Bay.…”

“…Horrocks et al 2007a, b) implying that, other than inferences from marine sediment cores (Wright et al 1995), relatively little is known about Northland environments during the period prior to MIS 2. Some information was however gained from a last c. 60 ka record from Lake Tangonge (Elliot et al 2005), a c. 80 ka discontinuous pollen record from Lake Omapere (Newnham et al 2004) and another discontinuous pollen record from Johnston's Gum Hole that commenced late in MIS 5 (D'Costa et al 2008). …”