Australian Lynch Crater Cautiously Hints Humanity Impacting Climate for last 45,000 Years

Contribution of organic matter molecular proxies to interpretation of the last 55 ka of the Lynch's Crater record (NE Australia)

Authors:

Kaal et al

Abstract:

The Lynch's Crater (NE Australia) deposit is a key information source on Late-Quaternary palaeoenvironmental change, including human-induced deforestation since the arrival of Aboriginals, megaherbivore extinction and southern hemisphere tropical climate dynamics. This study adds to the important dataset available for the site by assessing the molecular composition of organic matter in the record using pyrolysis–GC–MS to elucidate ecological and hydrological conditions since 55 ka BP.

Pyrolysates were dominated by methylene chain compounds (MCCs) and lignin products (methoxyphenols). Concomitant increases in MCCs and aquatic source indicators (biogenic opaline silica, Si:Al ratio, SEM-visible debris of sponges and diatoms and aquatic pollen taxa), which roughly coincide with abrupt climate events in GISP2 δ18O (Heinrich event H3, H1, 8.2 ka and oscillations at 33–36 ka BP), reflect transitions from peat (dominated by lignin from terrestrial plants) to lacustrine (MCCs from aquatic plants) conditions. The evidence points towards wet conditions causing the accumulation of layers rich in inorganic sediment during H events, favouring the hypothesis of a southward ITCZ shift, rather than an ENSO-induced northward shift, as the underlying mechanism. This contradicts previous studies using the “degree of peat humification” index (DPH). We measured DPH and the extracts and residues by PY–GC–MS, to better understand the validity of this surface moisture proxy. Paradoxically, high DPH corresponds to the relatively young (less than 15 ka) ombrotrophic peat environment, as DPH relies on the proportion of extractable carbohydrates concentrated in this part of the core, while deeper and unarguably more evolved layers are comprised of alkali-inextricable lignin and MCCs. Therefore, DPH does not accurately reflect humidity-controlled degradation/preservation dynamics and its use for studying climate change in complex records, such as Lynch's Crater, is cautioned. Finally, the decoupling of humidity conditions from changes in regional arboreal vegetation supports the hypothesis of an anthropogenic- rather than climate-driven shift towards sclerophyllous vegetation since 45 ka, but the hydroseral complexity of the system demands caution on this matter.

This is why I think the anthropocene idea is stupid.  This is another case where humanity has been impacting the climate long before the inane date of the modern concept.  In fact, there are suggestions humanity, whatever species you call us, has been doing so since we harnessed fire: Homo erectus may have been clearing forests intentionally for better habitat.