Testing the validity of productivity proxy indicators in high altitude Tso Moriri Lake, NW Himalaya (India)

• Investigations on catchment, vegetation, and lake surface sediments to identify end members for reconstructing past lacustrine primary productivity (LPP) in the Tso Moriri Lake.
• Data reveal limitations of using isotopic and C/N data on bulk organics as indicators of LPP.
• LPP in recent times is not much higher than during the early Holocene warm period ruling out the possibility of large carbon sequestration in high altitude oligotrophic lakes.

We use multiple proxies (δ13Corg, δ15Norg, C/N, amino acids, biogenic silica) from the catchment, lake surface and core sediments to (i) identify the factors influencing conventional lacustrine primary productivity (LPP) indicators (isotopic covariance, C/N) in the sediments from the pristine high altitude Tso Moriri Lake during the late Quaternary, (ii) compare C/N and bulk organic isotopic data from the core with available biogenic silica and amino acid data to test the applicability of conventional LPP indicators during the late Quaternary, and (iii) evaluate the degree of sensitivity of LPP to climate change. Our results show that climate driven changes in water salinity and source water changes have influenced the isotopic (δ13C, δ15N) content of the lake water and hence the isotopic composition of bulk organic matter. Erosion has also played a role in masking the LPP as the catchment sediments from this high altitude lake have low C/N thereby casting doubt on the effectiveness of this parameter as an LPP indicator. Independent LPP indicators in Tso Moriri sediments clearly indicate that it is driven by climate change and increases during warmer periods. However, our data show that the LPP in recent times is not much higher than during the early Holocene, ruling out any impact of recent warming on LPP and therefore the possibility of large carbon sequestration in high altitude oligotrophic lakes.