Monazite chemical weathering, rare earth element behavior, and paleoglaciohydrology since the last glacial maximum for the Loch Vale watershed, Colorado, USA

Abstract

Rare earth element (REE) release from weathering of accessory monazite [(REE)PO4] since the last glacial maximum at 18.1 ka was investigated in sediment recovered from an outlet lake within the glaciated Loch Vale watershed, Colorado, USA. Labile REEs in the sediments reveal monazite weathering increased during the Younger Dryas chronozone (YDC) 13.2 to 11.1 ka when alpine glaciers advanced as climate cooled and bedrock comminution increased. Monazite dissolution peaked at approximately the Pleistocene-Holocene transition ~10.5 ka. During the Holocene, REE concentrations decline, reflecting a reduction in monazite weathering. The REE cerium (Ce) may occur as trivalent or tetravalent cations, and the Ce anomaly (Cen/Ce*n) in sediment permits interpretations of paleoredox conditions. The Cen/Ce*n decreases from 18.1 ka to the Pleistocene-Holocene boundary. Initially, oxidizing conditions within the watershed increased because of enlargement of the proglacial area as the ice retreated. At the onset of the YDC, oxidation further escalated in response to enhanced chemical weathering associated with glacial advance. A more stable Holocene climate and landscape resulted in relatively small changes in Cen/Ce*n values. Slightly decreasing Cen/Ce*n values over the last several hundred years are consistent with present-day stream water values and may reflect the onset of present-day hydrobiogeochemical conditions.

Ecological Stoichiometry of the Mountain Cryosphere

“…Changes in downstream ecosystems induced by atmospheric warming will not be solely dependent on upstream deglaciation. Indeed, warmer temperatures will increase chemical weathering of bedrock minerals (e.g., calcite and apatite) which will subsequently alter water chemistry, particularly via increased N and P (Heath and Baron, 2014;Price et al, 2017). Rock glaciers, which are likely to be less affected by atmospheric warming and will therefore persist on the landscape longer than their surface counterparts (Knight et al, 2019), release solute-rich outflows into headwaters and labile C that can fuel heterotrophic production (Fegel et al, 2016(Fegel et al, , 2019.…”

Nutrients and warming interact to force mountain lakes into unprecedented ecological states

“…Phosphorus production has increased exponentially worldwide since 1950 [4], and regional mountain ecosystems in North America have received P-bearing minerals and organic compounds to North American mountains caused by dust and agricultural emissions (figure 4c; [9,11,83]). Increased weathering of P-bearing mineral apatite due to climate warming [84] and cryosphere thaw [85], might contribute P, as was suggested by Kopácěk et al [18] for granitic alpine catchments in the Tatra Mountains. Whether from atmospheric deposition or mineral weathering, an increase in P availability enhances algal productivity in most lakes [86].…”

Climatic controls on phosphorus concentrations in The Loch, Loch Vale Watershed, Rocky Mountain National Park, Colorado, USA since the last glacial maximum

“…The mineralogy and chemistry of the two units is nearly identical, with quartz, plagioclase (oligoclase An 27 ), microcline, and biotite as major minerals (Cole, 1977;Mast et al, 1990;Mast, 1992). Magnetite, ilmenite, garnet, epidote, apatite, monazite, zircon, orthopyroxene, calcite, and pyrite occur as minor minerals (Cole, 1977;Mast et al, 1990;Mast, 1992;Price et al, 2013Price et al, , 2017Price et al, , 2020.…”

“…1b; Baron, 1992b). The lake-bottom sediments are homogeneous gyttja with no sedimentary varves, laminations, or stratification visible in a split core (Price et al, 2017). Sediment enters The Loch via Icy Brook (Fig.…”

“…Lacustrine sediment cores have been collected from The Loch and analyzed for [P 5+ ] to investigate natural temporal changes through geologic time (Price et al, 2017). These lake-bottom sediments record the timing of glacial retreat from the end of the Pinedale glaciation through the Early Holocene, a time represented by the largest and most-punctuated climatic variability in the last 100,000 years (Lora and Ibarra, 2019;Quirk et al, 2020).…”