Influence of extreme storm events on West Florida Shelf CDOM distributions

Abstract

Colored Dissolved Organic Matter (CDOM) distribution and signatures provide vital information about the amount and composition of organic material in aquatic environments. This information is critical for deciphering the sources and biogeochemical pathways of organic carbon, and thus vital to the understanding of carbon cycling and budgets. Waters of the West Florida Shelf are heavily influenced by many river systems on Florida's Gulf Coast that, to the first order, control CDOM distributions on the shelf. Three storm events during 2004 and 2005 (Hurricane Charley, Hurricane Wilma, and a Winter Storm) profoundly altered the typical distribution of CDOM fluorescence and absorption properties on the Southern West Florida Shelf. Seasonal surveys revealed that changes in the underwater light field as a result of major hurricanes and resuspension events are linked closely with a number of factors prior to a storm's passing such as the presence of persistent blooms, rainfall and discharge. Additionally, storm track and wind direction were found to play a significant role in CDOM signatures.

Technical Note: Comparison of storage strategies of sea surface microlayer samples

“…On the other hand, Yamashita et al (2010b) found CDOM absorbance to be unaffected by freezing, although FDOM data were compromised, and Gao et al (2010) found that changes after freezing were less than 15 %. Other studies also found minimal effects of freeze/thaw on OM optical properties (Conmy et al, 2009;Yamashita et al, 2010a), and Spencer et al (2010) found that after freeze/thaw, changes in absorbance, spectral slope, specific UV absorbance, and fluorescence were within analytical error and always less than ±2 %.…”

“…Hunter and Liss (1981) found small SA losses from samples dark-stored at 6 • C for up to a week, but an increase of 20 % after 34 days. Freezing of filtered samples at −20 • C is also widely used for CDOM storage (Coble et al, 1998;Murphy et al, 2008;Conmy et al, 2009;Walker et al, 2009;Gao et al, 2010;Spencer et al, 2010;Yamashita et al, 2010b) but again sample provenance appears to be important; highly coloured samples comprising mostly allochthonous OM tend to show greater changes during freeze/thaw than more optically clear autochthonousdominated OM samples. Two studies of a range of freshwaters found that after freeze/thaw, fluorescence intensities and adsorption coefficients showed both increases and decreases (Spencer et al, 2007a;Hudson et al, 2009), although overall CDOM loss was observed and protein-, humic-, and fulvic-like fluorophore intensities all declined (Hudson et al, 2009).…”

Water clarity patterns in South Florida coastal waters and their linkages to synoptic-scale wind forcing

“…The secondary mode relates to shorter term Kd spikes associated with winter storms and extremely active weather situations with increased cold front passage and transitional wind fields. This was particularly evident during the winter storm event in December 2004 (Conmy et al, 2009), and the January-March 2010 event. Wind patterns during these events are speculated as major contributors to sediment resuspension/ transport and particle release from red tide or diatom blooms in nearshore waters and Kd spikes in the time series.…”

“…Excessive rainfall/discharge events in combination with seasonal and abrupt storm and cold front passage can force sediment and particle resuspension, alter CDOM and nutrient delivery into the coastal zone and trigger changes in the water column constituents that impact clarity (Hu et al, 2006;Hu et al, 2003;Hu et al, 2004;Le et al, 2013;Lohrenz et al, 1999;Ransibrahmanakul and Stumpf, 2002;Barnes et al, 2013;Lee et al, 2002). Excessive and widespread phytoplankton blooms and ''black water'' events contribute substantially to changes in water column constituents (Hu et al, 2003;Hu et al, 2004;Hu et al, 2006;Conmy et al, 2009;Neely et al, 2004). Conmy et al (2009) attributed major changes in the underwater light field of the West Florida Shelf (WFS) to tropical and extratropical storms, discharge, and resuspension events, hinting at the profound influence of wind forcing on water constituents in the region.…”

“…Excessive and widespread phytoplankton blooms and ''black water'' events contribute substantially to changes in water column constituents (Hu et al, 2003;Hu et al, 2004;Hu et al, 2006;Conmy et al, 2009;Neely et al, 2004). Conmy et al (2009) attributed major changes in the underwater light field of the West Florida Shelf (WFS) to tropical and extratropical storms, discharge, and resuspension events, hinting at the profound influence of wind forcing on water constituents in the region. The overall influence of synoptic systems such as storms and cold fronts in combination with discharge, winds and transport likely co-contribute to water clarity changes at sub-regional scales, especially in Florida Shelf and Florida Keys systems where upwelling/mixing and transport of materials "downstream" of river sources can occur (Del Castillo et al, 2000;Hu et al, 2004;Lee et al, 2002;Gramer, 2013).…”