Estero Bay is located in southwest Florida in Bonita Beach and is geologically very young at approximately 5,000 years old. It is fed by three water systems: the Hendry and Mullock Creek, Estero River, and the Imerial River. These systems supply freshwater and sediment deposits to the bay and may have a major impact on the sediment composition depending on location. Another powerful landscaping force is the rise and fall of sea level. Common features that revolve around these landforms include inner bay margins, inner bay islands, barrier islands, and flood tidal delta islands. Cores were taken at two locations in the bay: core one or the "back barrier" core, and core three or the "inner bay margin."
Core one was located on the sheltered side of a barrier island, or in the "back barrier" area. The total length of the core was 220.5 cm and the compaction rate was 15.9%. The bottom of the core was rich in organic matter and dark, fine, well sorted sand, indicating that at that time, the location was most likely a protected bay, with low wave energy, allowing fine particles to settle, and a nearby inlet that provided these fine sediment deposits. Within this section is a short over wash deposit band of sandy sediment that has shell material at the bottom and gradients up to a light colored sand. This punctuation ends after about 3 cm and the dark sediment described above resumes until it hits an air pocket that was filled with water until the corer was sliced in half; this may be due to imperfect sampling techniques. At about a depth of 109.7 to 52.4 cm, there is a sand-shell-sand-shell alternating layer, which indicates a possible shift from a more protected area, to an area that is more effected by tides. The sediment is poorly sorted, which indicates a higher level of disruption. Perhaps a barrier island that previously sheltered the bay was flooded or destroyed, allowing for a less protected area to develop. Next, there is a band of sandy soil that indicates the area was a beach or barrier island for a period of time. Then, the sediment composition indicates a shift back to fine sand, with some productivity indicated by shell fragments. Then, there is another short disruptive band, which may also indicate a storm event. However, this storm band is coarser than the first, which correlates with the idea that the bay is less protected and there was higher wave action. Finally, the top layer is composed of dark, fine sand and silt, rich in organic material.
Core three was located on the "inner bay margin" in a more open location, but still close to mangroves. The core length was 159.0 cm and the compaction rate was 51.6%. The bottom layer is composed of peat, indicating that the location was dominated by organic matter and mangrove habitat. Next follows a layer of large shell material with dark gray sands. This high level of organic productivity indicates that the sea level was rising and pushing the mangrove habitat up. This lagoon setting seems to become more freshwater over time because the marine organisms seem to disappear as the core goes up. The barrier islands may be more pronounced, trapping the freshwater flow from rivers and letting less marine water in through inlets, leading to a decrease in marine organisms. The sediment particles themselves seem to remain fairly consistent throughout, but the productivity and amount of gastropods and bivalves decreases as the core progresses upward, which parallels the predicted general decrease in salinity over time. The top layer has little to no productivity and indicates a low energy wave system. There are three bands punctuating the core sample that indicate potential disturbances from storms, but the bands aren't noteworthy in their differences. The compaction rate for this core is much greater than the first probably due to the type of sediment and the air/water pocket in the first sample. Overall, it can be concluded that the first core was most heavily influenced by the surrounding barrier islands, and the third core was heavily dictated by sea level rise.
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| The approximate location of core 1 |
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| The approximate location of core 2 |
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| A picture showing some of the core layers |
Nice photos, but is the top of the core at the bottom of the picture?
ReplyDeleteNo, the bottom of the core is at the bottom of the picture. The core was way too long to fit in one picture, so I just took a close up of the end of it, because there were some interesting bands at the bottom.
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