Climatic and lacustrine morphometric controls of diatom paleoproductivity in a tropical Andean lake

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Climatic and lacustrine morphometric controls of diatom paleoproductivity in a tropical Andean lakeAuthor(s)
Date
2015-12Citation
Bao, R., Hernández, A., Sáez, A., Giralt, S., Prego, R., Pueyo, J.J., Moreno, A., Valero-Garcés, B.L., 2015. Climatic and lacustrine morphometric controls of diatom paleoproductivity in a tropical Andean lake. Quaternary Science Reviews 129, 96-110. doi: 10.1016/j.quascirev.2015.09.019
Abstract
The coupling of lake dynamics with catchment biogeochemistry is considered the key element
controlling primary production in mountain lakes at time scales of a few decades to millennia, yet little
is known on the impacts of the morphometry of lakes throughout their ontogeny. As Lake Chungará
(Central Andean Altiplano, northern Chile) experienced long-term lake-level fluctuations that strongly
modified its area:volume ratio, it is an ideal system for exploring the relative roles that long-term
climatic shifts and lake morphometry play on biosiliceous lacustrine productivity. In this paper, we
review previous data on the percent contents of total organic carbon, total inorganic carbon, total
nitrogen, total biogenic silica, isotopic composition of organic matter, carbonates, and diatom frustules,
as well as data on the abundance of the chlorophycean Botryococcus braunii in this lake for the period
12,400-1,300 cal yr BP. We also include new data on organic carbon and biogenic silica mass
accumulation rates and the diatom assemblage composition of an offshore core dated using 14C and
U/Th.
Biosiliceous productivity in Lake Chungará was influenced by shifts in allochthonous nutrient inputs
related to variability in precipitation. Humid phases dated at approx. 12,400 to 10,000 and 9,600 to
7,400 cal yr BP coincide with periods of elevated productivity, whereas decreases in productivity were
recorded during arid phases dated at approx. 10,000 to 9,600 and 7,400 to 3,550 cal yr BP (Andean
mid-Holocene Aridity Period). However, morphometry-related in-lake controls led to a lack of a linear
response of productivity to precipitation variability. During the late Glacial to early Holocene, lowstands
facilitated complete water column mixing, prompting episodic massive blooms of a large centric
diatom, Cyclostephanos cf. andinus. Thus, moderate productivity could be maintained, regardless of
aridity, by this phenomenon of morphometric eutrophy during the early history of the lake. The
subsequent net increase in lake level introduced modifications in the area of the epilimnion sediments
versus the total volume of the epilimnion, preventing complete overturn. Surpassing a certain depth
threshold at approx. 8,300 cal yr BP caused cessation of the morphometric eutrophy conditions
associated with Cyclostephanos cf. andinus superblooms. After 7,300 cal yr BP, the lake experienced
a decrease in biosiliceous productivity and a change of state that involved a stronger dependence on
3
precipitation variability, with a lesser contribution of diatoms to the total primary productivity. Our
results show that the interpretation of lacustrine paleoproductivity records as paleoclimatic archives
needs to take into account the effects of changes in the epilimnion sediment area to epilimnion volume
ratio in association with lake ontogeny.
Keywords
Laminated sediments
Holocene
Lake paleoproductivity
Lake ontogeny
Andean Altiplano
Diatoms
Limnogeology
Paleoclimate
Paleolimnology
Paleoecology
Holocene
Lake paleoproductivity
Lake ontogeny
Andean Altiplano
Diatoms
Limnogeology
Paleoclimate
Paleolimnology
Paleoecology
Editor version
ISSN
1873-457X