A 1000-year record of paleoclimate and paleoenvironment change inferred from sedimentary organic matter in Lake Azuei, Haiti

2023

Article référencé dans le Web of Science WOS:001153685900001

Noncent D., Sifeddine Abdelfettah, Emmanuel E., Cormier M. H., Briceño-Zuluaga F. J., Valdés J., Mendez-Millan Mercedes, Turcq Bruno, Bernal J. P.

Palaeogeography Palaeoclimatology Palaeoecology, 2023, 632, 111845 [9 p.] ISSN 0031-0182

We studied sediment organic matter (OM) to reconstruct the environment over the last millennium using a sediment core from Lake Azuei, Haiti, also known as "Etang Saumatre." Chronology for the 84-cm-long core was established with 11 14C dates and 210Pb analysis. Total organic carbon (TOC) concentrations in the sediment were low (0.58 - 4.89%), as were total nitrogen (TN) values (0.06 - 0.40%). Carbon isotopic ratio (delta 13C) values were relatively negative and C/N ratios were low, suggesting that algae and terrestrial C3 plants were the primary sources of OM in the lake sediment. The inverse relationship between the nitrogen isotopic ratio (delta 15N) and TOC is related to denitrification in the sediment. We identified five stratigraphic zones using a delta 13C vs. C/N cross diagram: 1) Medieval Climate Anomaly 1 (MCA1) (1000-1050 CE), 2) Medieval Climate Anomaly 2 (MCA2) (1050-1100 CE), 3) Transition period between Medieval Climate Anomaly and Little Ice Age (MCA-LIA) (1150-1400 CE) 4) Little Ice Age (LIA) (1400-1800 CE), 5) Current Warm Period (CWP) (1800-2000 CE). These stratigraphic zones correspond to three climate episodes. The first was applied MCA1 and LIA periods, when there was a decrease in TOC and TN as well as in plankton-derived OM. This was accompanied by an increase in delta 15N, which suggests denitrification due to suboxic conditions, likely caused by an increase in lake water temperature and dry conditions. The second climate episode was the MCA-LIA transition period and was characterized by high variability of TOC, delta 13C and delta 15N. The organic matter deposited during this period appeared to be a mixture of material originating from both autochthonous phytoplankton and allochthonous C3 plants. There was climate instability during this period, with alternations between wet and dry conditions, and thus likely variations in lake level. The third climate episode, the MCA2 and CWP periods, was characterized by an increase in TOC and TN values, and decrease in delta 13C and delta 15N values. This was chiefly attributable to more organic material input which was derived from C3 terrestrial vegetation growing around the lake. A decrease in delta 15N indicated a reduction in denitrification, further suggesting an increase in the input of organic matter. Sedimentation during these periods occurred when there was more transport related to wet conditions.

Sciences du milieu [021] ; Géologie et formations superficielles [064]

HAITI

Fonds IRD [F B010089470]

fdi:010089470