Peat humification records from Restionaceae bogs in northern New Zealand as potential indicators of Holocene precipitation, seasonality, and ENSO

Abstract

In comparison with temperature reconstructions, New Zealand proxy records for paleo-precipitation are rare, despite the importance of precipitation in contemporary climate variability and for projected climate impacts. In this study, records of mid-late Holocene palaeomoisture variation were derived for two hydrologically separate ombrotrophic Restionaceae bogs in northern New Zealand, based on peat humification analysis. At each site, three cores were analysed for peat humification, facilitating both intra-and inter-site comparisons. Age models for the six sequences were developed using radiocarbon dating and tephrochronology. Twelve tephras (including six cryptotephras) were recognised, four of which were used to precisely link the two sites and to define start and end points for the records at 7027 ± 170 (Tuhua tephra) and 1718 ± 10 cal. yr BP (Taupo tephra) (2σ-age ranges), respectively.We find individual differences between the six peat humification records at short-term timescales that are presumably due to local site factors, in particular changing vegetation and microtopography, or to changes in the composition of the material analysed. Stronger longer-term coherence is observed between all six records but is attributed to slow anaerobic decay over time because the implied trend towards wetter 2 summers in the late Holocene cannot be corroborated by independent climate proxies. Despite these confounding factors, centennial scale shifts in bog surface wetness are a pervasive feature of all six records with varying degrees of overlap in time that show strong correspondence with El Niño-Southern Oscillation reconstructions from the eastern equatorial Pacific. These results indicate the potential for peat humification records from New Zealand's ombrotrophic bogs to elucidate past climate variability and also demonstrate the importance of developing multiple well-dated profiles from more than one site.

Four peat humification-recorded Holocene hydroclimate changes in the southern Altai Mountains of China

“…Although this is a sound conceptual basis, questions have been raised about the general applicability of humification as a paleoclimatic or paleohydrological proxy because the humification-based peat-surface wetness reconstructions have been challenged by other proxies-based peat moisture records (Amesbury et al, 2012; Chambers et al, 2011; Hughes et al, 2012; Newnham et al, 2019; Yeloff and Mauquoy, 2006). The inconsistencies between humification and other proxies are most likely attributable to two reasons: (1) site-specific changes in peat botanical composition (Chambers et al, 1997; Hughes et al, 2012; Payne and Blackford, 2008; Zhang et al, 2017) and (2) locality-specific variations in topography and geochemistry of peat (Caseldine et al, 2000; Morgan et al, 2005).…”

“…The inconsistencies between humification and other proxies are most likely attributable to two reasons: (1) site-specific changes in peat botanical composition (Chambers et al, 1997; Hughes et al, 2012; Payne and Blackford, 2008; Zhang et al, 2017) and (2) locality-specific variations in topography and geochemistry of peat (Caseldine et al, 2000; Morgan et al, 2005). Newnham et al (2019) also challenged the use of humification and found that stronger longer-term trend of humification is attributed to slow anaerobic decay over time because the trend toward wetter summers in the late Holocene cannot be corroborated by independent climate proxies.…”

“…Peat humification-climate researches have been mostly undertaken in North Europe (Amesbury et al, 2012; Borgmark and Wastegård, 2008; Vorren et al, 2012), East Asia (Hong et al, 2001; Ma et al, 2008; Wang et al, 2004; Xiao et al, 2017), North America (Payne and Blackford, 2008), Australia and New Zealand (Burrows et al, 2014; Jara et al, 2017; Newnham et al, 2019; Viau and Gajewski, 2009; Wilmshurst et al, 2002). In Central Asia, the work of peatland research gained more international recognition in recent decades due to several high-resolution alpine ombrotrophic peatlands (e.g.…”

TephraNZ: a major and trace element reference dataset for prominent Quaternary rhyolitic tephras in New Zealand and implications for correlation

“…Lowe, 1988;Shane and Hoverd, 2002;Molloy et al, 2009;Shane et al, 2013;Hopkins et al, 2015Hopkins et al, , 2017Peti et al, 2020) (3) Bog settings (e.g. Lowe, 1988;Newnham et al, 1995Newnham et al, , 2007Newnham et al, , 2019Lowe et al, 1999Lowe et al, , 2013Gehrels et al, 2006), or (4) within terrestrially exposed (commonly marine or riverine) sediments, for example in the -Whanganui Basin (e.g. Seward, 1976, Naish et al, 1996Pillans et al, 2005;Rees et al, 2019), 140 -Wairarapa region (e.g.…”

Characterization of porous microaggregates and soil organic matter sequestered in allophanic paleosols on Holocene tephras using synchrotron-based X-ray microscopy and spectroscopy

“…The central North Island of New Zealand has huge stores of buried, allophane-rich paleosols developed on sequences of well-dated tephra beds 16,17,23,24 . The early Holocene of this region was dominated by extensive podocarp-broadleaf forest and warm and wet conditions followed generally by gradual drying and cooling [25][26][27][28] with modest uctuations 29 . Thus, the slow carbon turnover rate in allophane-rich soils, and the abundance of buried allophanic paleosols on dated tephras in North Island, provide the opportunity to characterize the nature of stabilized SOM preserved in allophanic soils/paleosols in response to changes of environmental and climatic conditions.…”