Environmental changes in northern New Zealand since the Middle Holocene inferred from stable isotope records (δ15N, δ13C) of Lake Pupuke

Abstract

Maar lakes in the Auckland Volcanic Field are important high-resolution archives of Holocene environmental change in the Southern Hemisphere mid-latitudes. Stable carbon and nitrogen isotope analyses were applied on bulk organic matter and the green alga Botryococcus from a sediment core from Lake Pupuke (Auckland, North Island, New Zealand) spanning the period since 7,165 cal. year BP. The origin of organic matter was established using totalorganic-carbon-to-nitrogen ratios (TOC/TN) as well as organic carbon (d 13 C OM ) and nitrogen (d 15 N) isotope composition of potential modern sources. This approach demonstrated that the contribution of allochthonous organic matter to the lake sediment was negligible for most of the record. The sedimentary TOC/TN ratios that are higher than Redfield ratio (i.e.[7) are attributed to N-limiting conditions throughout the record. Variations of nitrogen and carbon isotopes during the last 7,165 years are interpreted as changes in the dominant processes in the lake. While epilimnetic primary productivity controlled isotope composition before 6,600 cal. year BP, microbial processes, especially denitrification and methane oxidation, caused overall shifts of the d 15 N and d 13 C values since the Mid-Holocene. Comparisons with climate reconstructions from the Northern Island suggest that changes in the wind-induced lake overturn and a shift to more pronounced seasonality were the most likely causes for lake-internal changes since 6,600 cal. year BP.

Holocene history of human impacts inferred from annually laminated sediments in Lake Szurpiły, northeast Poland

“…Periodic or seasonal anoxia in hypolimnetic water is indicated by low values of d 13 C org and high Fe/Mn (Fig. 4c), which can be interpreted as resulting from microbial and/or methanogenic biomass (Heyng et al 2012). Human impact increased slowly at the end of this phase, which coincides with the age of the oldest anthropogenic colluvium in the Suwałki region (Smolska and Szwarczewski 2008).…”

The stable isotope composition of organic and inorganic fossils in lake sediment records: Current understanding, challenges, and future directions

“…When the organic matter produced within lakes by aquatic macrophytes and algae is an important component of SOM, the stable isotope composition of SOM and algae (e.g. Botryococcus) are strongly coupled, even on millennial time scales (Heyng et al 2012). In a study of 40 lakes on the Tibetan Plateau d 13 C values of aquatic macrophytes correlated positively with d 13 C values of SOM, although much stronger correlations existed between d 13 C values of Potamogeton and d 13 C values of mid-chain n-alkanes, which are largely produced by the macrophytes (Aichner et al 2010).…”

Topical advances and recent studies in paleolimnological research

“…Lake evolution and development were examined in the context of changing climate regimes (Väliranta et al, 2011;Kaufman et al, 2012;Terasmaa et al, 2013). Recent studies reported changes in stratification and mixing patterns in response to climate change (Lennox et al, 2010;Kaufman et al, 2012;Gallaway et al, 2011;Heyng et al, 2012;Stephens et al, 2012a). Shifts between wet and dry climate cycles were shown to cause changes in erosion and sedimentation patterns (Vogel et al, 2010;Holmgren SU et al, 2012;Bjerring et al, 2013).…”

“…Shifts between wet and dry climate cycles were shown to cause changes in erosion and sedimentation patterns (Vogel et al, 2010;Holmgren SU et al, 2012;Bjerring et al, 2013). Studies examined the influence of climate on organic matter sources (Heyng et al, 2012), on primary productivity, and on eutrophication (Kaufman et al, 2012;Vogel et al, 2010;Stephens et al, 2012a;Scussolini et al, 2011;Zahner et al, 2013). Galloway et al (2011) reported the effects of climate change on lake salinity in British Columbia based on diatom and pollen evidence.…”