Seasonal controls on sediment transport and deposition in Lake Ohau, South Island, New Zealand: Implications for a high‐resolution Holocene palaeoclimate reconstruction

Abstract

Laminated sediments in Lake Ohau, Mackenzie Basin, New Zealand, offer a potential high‐resolution climate record for the past 17 kyr. Such records are particularly important due to the relative paucity of detailed palaeoclimate data from the Southern Hemisphere mid‐latitudes. This paper presents outcomes of a study of the sedimentation processes of this temperate lake setting. Hydrometeorological, limnological and sedimentological data were collected over a 14 month period between 2011 and 2013. These data indicate that seasonality in the hydrometeorological system in combination with internal lake dynamics drives a distinct seasonal pattern of sediment dispersal and deposition on a basin‐wide scale. Sedimentary layers that accumulate proximal to the lake inflow at the northern end of the lake form in response to discrete inflow events throughout the year and display an event stratigraphy. In contrast, seasonal change in the lake system controls accumulation of light (winter) and dark (summer) laminations at the distal end of the lake, resulting in the preservation of varves. This study documents the key processes influencing sediment deposition throughout Lake Ohau and provides fundamental data for generating a high‐resolution palaeoclimate record from this temperate lake.

Hydrological thresholds and basin control over paleoflood records in lakes

“…At Brotherswater, high flows introduce water warmer than that of the lake (Fig. 1C); the diffusion of these less dense hypopycnal plumes represents the dominant sediment dispersal pathway, differing from cold, dense winter hyperpycnal flows dispersing materials in turbulent suspension across the profundal basin in polar and montane lakes (Gilbert et al, 2006;Cockburn and Lamoureux, 2008;Roop et al, 2015). The December 2012 event delivered more coarse material to the upper traps (Fig.…”

Morphological expression of bedforms formed by supercritical sediment density flows on four fjord‐lake deltas of the south‐eastern Canadian Shield (Eastern Canada)

“…Hyperpycnal flows (underflows) can be generated when freshwater charged with sediment plunges to form sediment density flows (or density flows sensu Talling et al ., ) in the receiving basin (Mulder & Syvitski, ). When river water density is lower, coarse sediments accumulate on delta fronts and fine particles propagate into receiving basins as hypopycnal or homopycnal flows (Cockburn & Lamoureux, ; Roop et al ., ). In addition, the accumulation of sediment on delta fronts may reduce slope stability, favouring the generation of slope failures that evolve into turbidity currents downslope (Girardclos et al ., ; Hughes Clarke et al ., ).…”

Low-resolution Australasian palaeoclimate records of the last 2000 years

“…Nonetheless, it is clear from the New Zealand proxy assemblages that the presence of tephras and pollen markers can improve the chronostratigraphic constraints associated with 14 C dates as applied in many cores. Some sites also show potential to be revisited to improve age controls, sample at higher resolution, and calibrate proxy data against instrumental records to develop a reliable climate reconstruction (Roop et al, 2015).…”

“…Site monitoring Roop et al, 2015;Tibby et al, 2003), climate sensitivity studies (Bertrand et al, 2002;Neukom and Gergis, 2012), and proxy systems models (Dee et al, 2016;Evans et al, 2013) are approaches that increase confidence in the type and strength of climate signal expressed by a proxy. These approaches would also help to improve the interpretation of previously published work in Australasia.…”