Order 1411304: Oceanography

Silicon levels in Mobile Bay and the Gulf of Mexico

I. Introduction

Silicate is a very important nutrient in the ocean. Silicate is essential for diatoms, particularly, and also for sponges and radiolarians. Even though sponges are benthic, many use silicate to support their structure. Radiolarians are microscopic.

Diatoms are also microscopic and photosynthetic organisms. Areas that are surrounded by rivers receive a great deal of volume of sediment at a very high delivery rate (Davis, 2017). Nearly five million metric tons of large amounts of sediment are carried into Mobile Bay every year (Davis, 2017). While 33% of it stays in the delta at the mouth of the Mobile River, half of it settles to the bottom of Mobile bay. Only about 15% of it makes it into the gulf (Davis, 2017). Silicate is very specifically important for diatoms, siliceous sponges and radiolarians.

The majority of how Silicate returns back into the ocean is through weathering and fresh water sends it back towards the ocean through rivers. Given the large amount of fresh water input in Mobile Bay, I hypothesize that Silicate levels will be significantly higher in Mobile Bay than the samples that were taken from the Gulf of Mexico.

II. Materials and Methods

Samples were collected on June 12th and nutrient samples were taken at five different stations. At each station samples were collected at three different depths; surface, middle, and deep. The Niskin collected water at each depth. 60 mL of unfiltered water was collected each depth and filtered through. 15 mL of the sample was saved and store on ice until returned to the lab. The sampling started in Mobile Bay and we continued to work our way south towards the Gulf of Mexico. CTD data was processed by DISL tech support and then provided to us.

III. Results

The Silica results show higher levels at the surface than in the deep waters in both the bay and the gulf. The only station that did not show this same result was the very last station (station #12). The surface water had 18.02 umol Si/liter and the deep water had 25.45 umol Si/liter. This was the only station that had a higher level of Si at the bottom compared to the surface. We were not able to conduct data from the middle depth at the first station. All of the stations appeared to have close levels from the middle depth to its deep depth. The surface levels for Si starting at the bay and going south towards the gulf of mexico started at 78.0 umol/L at station 1, 77.34 at station 3, 82.34 at station 6, 60.71 at station 9, and 18.02 at station 12. At station 1 the deep depth was 29.83 umol/L, station 3 was 21.55 umol/L, station 6 was 14.42 umol/L, station 9 was 15.61umol/L, at station 12 was 25.45 umol/L.

Station #	Depth	Si- Results[umol Si/liter]
1	surface	78.10
1	middle	-999.00
1	deep	29.83
3	surface	77.34
3	middle	22.91
3	deep	21.55
6	surface	82.34
6	middle	17.70
6	deep	14.42
9	surface	60.71
9	middle	12.13
9	deep	15.61
12	surface	18.02
12	middle	1.62
12	deep	25.45

IV. Discussion

So overall, the surface level throughout Mobile Bay and The Gulf of Mexico was not significantly higher until the last station in the gulf. The highest surface level was at station 6 at 82.34 umol/L and the lowest was at the last station (station 12) at 18.02. Other than station 12, the numbers remained fairly close. The bottom depth levels throughout the bay and gulf was significantly lower numbers compared to the surface levels. The highest level at the deepest depth was at station 1 at 29.83 umol/L and the lowest level was at station 6 at 14.42 umol/L.

V. Works Cited

Davis R.A. (2017) Sediments of the Gulf of Mexico. In: Ward C. (eds) Habitats and Biota of the Gulf of Mexico: Before the Deepwater Horizon Oil Spill. Springer, New York, NY

Zhao Y, Quigg A (2014) Nutrient Limitation in Northern Gulf of Mexico (NGOM): Phytoplankton Communities and Photosynthesis Respond to Nutrient Pulse. PLoS ONE 9(2): e88732. https://doi.org/10.1371/journal.pone.0088732