Mineral Secrets of Lake-Azuei: Reconstructing 1000 Years of Haitian Hydroclimate

 

The Caribbean climate is shaped by complex interactions between Atlantic and Pacific climate systems. Understanding these influences is crucial not only for interpreting past climate changes in Haiti but also for predicting future regional and global trends. This study employed techniques like inorganic compositional analysis, mineralogical analysis, and organic carbon analysis to reconstruct climate variability in Haiti over the past millennium. While previous studies have provided insights into Haiti's climate history over longer periods, this research specifically focuses on the past thousand years. It aims to determine how climate modes like AMO, NAO, PDO, and ENSO influenced this variability. Understanding these influences is crucial not only for interpreting past climate changes in Haiti but also for predicting future regional and global trends.

 

Study site

This study focuses on sediment core LA17BCO2 collected in January 2017 from Lake Azuei, also known as Étang Saumâtre, Haiti's largest lake. Located in the Cul-de-Sac watershed east of Port-au-Prince, the lake has seen a significant increase in area since the late 20th century. The narrow lake measures 22 km northwest to southeast, with a maximum width of 12 km and a depth of 30 meters. It is also situated in one of Haiti's driest regions and is highly sensitive to precipitation changes. It rests on an alluvial plain surrounded by carbonate mountains and straddles a major geological fault line.

 

Materials and method

 

Core Sampling and Analysis

This is a method used to analyze a sediment core retrieved from the Lake. A piston rod corer collected an 84cm-long core (LA17BCO2) from 19.8m water depth while samples were taken every 2 cm (except for radioisotope dating sites), totaling 32 for analysis.

 

Dating:

Several steps are important for dating. Radiocarbon dating of shells, wood, and organic matter revealed the core's age. High-resolution 210Pbxs measurements dated the top 10 cm more precisely. Calibration software converted radiocarbon ages to calendar years.

 

Analysis Techniques

·         Physical characteristics were examined including color, bands, and laminae structures both on a large and small scale.

·         The gray level is also measuring by using ImageJ software to analyze a high-resolution photo of the core, assigning each pixel a gray level value between 0 (black) and 255 (white).

·         wavelet analysis is also proceeded. This technique helps identify dominant frequencies (patterns) within the gray level data, revealing hidden periodicities in the sediment layers.

·         Major and trace elements (Ca, Al, Fe, etc.) were measured using ICP-MS after acid digestion.

  • X-ray diffraction identified and quantified minerals like calcite, Mg-calcite, aragonite, quartz, and clays.
  • Organic carbon content was measured using an elemental analyzer after removing carbonates.

 

Results

Chronology and Sedimentation

Radiocarbon dating in Lake Azuei is inaccurate due to "hard-water-lake error" (HWLE). This means "old" carbon from dissolved rock dilutes the younger "radioactive" carbon, making dates appear older. Radiocarbon dating corrected for "hard-water lake error," revealed age variations over the core's 6-7 centuries timeframe. A combination of radiocarbon and 210Pb dating has established a detailed age-depth model.

 

Lithology and Gray Level:

Different sediment layers were visually identified, with variations in clay, organic matter content, and color (darker upper layers representing higher organic matter). Gray level data showed high variations, with brighter colors in lower sections and distinct intervals of high fluctuations.

Mineralogical Composition

Calcite, Mg-calcite, and aragonite were the dominant minerals throughout the core. Ca-calcite, quartz, and clays exhibited similar behavior, negatively correlated with Mg-calcite while aragonite showed minimal variation.

Geochemical Composition:

Calcium was the most abundant element, reflecting high calcite content. Other elements (Al, Fe, K, Ti, Zr) correlated with each other and negatively with Ca, suggesting their common terrigenous origin and influence from water balance components. Organic carbon content varied, with a slight increase in topmost sediments, and showed an opposite trend to Ca.

 

Conclusion

In brief, studying calcium carbonate variations in lake sediments can reveal past climate changes. While core reflects the amount of organic and inorganic material present. Lighter colors indicate more terrigenous input (soil washed into the lake), while darker colors indicate less. This suggests a drier climate during periods with less terrigenous input and a wetter climate during periods with more terrigenous input. This understanding is critical for developing effective adaptation strategies and mitigating the impacts of future climate change in Haiti. This study contributes to a broader effort to understand and predict climate changes in the Caribbean and beyond. By delving into the past, we can gain valuable insights that will help navigate the challenges of a changing climate in the future.

 


DOI: https://doi.org/10.1177/09596836231163512

 

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