Data on sea surface biophysical parameters during different monsoon seasons

The biophysical data presented in this article were collected in the east coast of Peninsular Malaysia from May to November 2009. These monthly surface data were obtained from 32 stations along the coastal-offshore transect and were analyzed to understand the spatial and temporal distributions of biophysical parameters during different monsoon seasons. The data presented here include sea surface temperature (SST), sea surface salinity (SSS), Secchi disk depth (SDD), Chlorophyll-a (Chl-a), suspended particulate matter (SPM), mineral suspended solid (MSS) and chromophoric dissolved organic matter (CDOM).


Data
The dataset included in this article consists of 2 Tables and 1 Figure that represent the spatiotemporal distribution of surface biophysical parameters. Table 1 summarizes the details of the sampling locations (longitude and latitude) and depths. The monthly variations sea surface temperature (SST), sea surface salinity (SSS), Secchi disk depth (SDD), chlorophyll-a (Chl-a), suspended particulate matter (SPM), mineral suspended solid (MSS) and chromophoric dissolved organic matter (CDOM) are presented in Table 2 and Fig. 2. SST and SSS during the measurement period ranged from 28.2 C to 32.0 C and from 22.3 psm to 33.2 psm, respectively. Relatively high SST and SSS were recorded in May and July, respectively, while low values for both parameters were measured in November. Similarly, relatively low SDD was recorded in November and there were considerable fluctuations between the monsoon seasons, ranging from 1.0 m to 31.3 m (October) ( Table 2 and Fig. 1). All optically active constituents (Chl-a, SPM, MSS and CDOM) showed clear seasonal variations, with minimum values during the inter-monsoon (May and October) and Southwest monsoon (June to August) and maximum values during the northeast monsoon (November). Chlorophyll-a concentrations varied between 0.11 mg/l (October) and 7.74 mg/l (November) and SPM between 0.20 (August) and 22.80 mg/l (November).
The interrelationships among certain biophysical parameters are presented in Fig. 2. These relationships indicate a strong non-linear correlation among optically active constituents (Chl-a, SPM, MSS and CDOM); and between SDD and optically active constituents.

Experimental design
The stations were sampled between May 2009 and November 2009 under various environmental conditions during different monsoon seasons. The sampling dates (Table 3) coincide with 3 major monsoon seasons, the southwest monsoon (June to August), northeast monsoon (November) and inter-monsoon (May and October). Although it is difficult to determine the actual timing of each monsoon onset, the monsoon intra-seasonal oscillation is relatively repeatable with each monsoon onset can vary by two to three weeks from year to year [1,2]. The data were collected along inshore-Specifications Table   Subject  Earth and Planetary Sciences  Specific subject area  Oceanography  Type of data  Tables  Figures  How data were Fig. 3). The distance between the sampling stations for each transect varies from 5 km at the coastal stations (the first 3 stations) to 9 km at the seaward stations (Fig. 3). All stations were sampled during each cruise except for stations 1e7 in May and October due to weather conditions. For all measurements, water samples were collected from approximately 0.2e0.3 m depth using a submersible water pump into 10 l dark bottles. The entire sampling was done in the daytime only (9.30 a.m.e4.00 p.m.).

Oceanographic parameters
Basic oceanographic parameters of temperature and salinity were measured at each sampling station using two different types of instrument; a SBE 911 CTD profiler and a Yellow Springs Instruments (YSI) 6600 Multi Parameter V2 Sonde. In situ Secchi disk depth (SDD) was determined at each station using a conventional black and white Secchi disk with a diameter of 50 cm.

Chlorophyll-a
At each sampling station, only one replication of water sample was collected for the chlorophyll-a measurement. Chlorophyll-a concentration was determined spectrophotometrically using a Cary-100 double beam Spectrophotometer (Agilent Technologies). A known volume of water (1e5 L depending on particle load) was filtered under low vacuum pressure (300e400 mmHg) onto 47-mm Whatman Table 1 Location of sampling stations.

Station
Longitude (   glass-fibre filters (GF/F) with pore size 0.7 mm. Samples were subsequently kept on ice after collection and stored in the dark until analysis in the laboratory. The particulate matter retained on the filters was extracted in 10 ml volume of 90% acetone and refrigerated between 8 and 24 hours. The trichromatic equations [3] were used to calculate concentrations of chlorophyll.

Suspended particulate matter and mineral suspended solid
Three replicates of water samples were collected from surface water at each station. Filters were washed with 250 ml of distilled water after filtration to remove any trace of salt and were immediately stored cooled until analyzed. Suspended particulate matter (SPM) was measured gravimetrically on pre-weighed and pre-combusted 0.7 mm GF/F filters (450 C for 4 hours). Filters were oven-dried at 75 C for 24 hours [4], cooled to room temperature and reweighed on the same balance (0.1 mg precision) to obtain SPM. The filters were then re-combusted at 450 C for 4 hours and reweighed again to obtain mineral suspended solid (MSS).

Chromophoric dissolved organic matter (CDOM)
Samples for CDOM were collected by filtering 150e200 ml of water through 0.2 mm Whatman Nucleopore polycarbonate filters into pre-acid washed and pre-combusted amber glass bottles [4]. For this parameter, only one sample was collected for each station. The filtrates were stored frozen for  Table 3 Dates of in situ measurements.

Start date
End date Description analysis in the laboratory and were analyzed within 1 week of collection. CDOM absorption (a g ) was measured using a Cary-100 dual beam Spectrophotometer using a 10 cm cylinder cuvette and corrected with a Milli-Q blank. The measured absorbance data were normalized to zero at wavelengths between 750 and 800 nm to remove temperature related measurement artifacts [5]. The absorption coefficient at 443 nm was selected as a reference wavelength to represent the CDOM concentration as calculated from Eq. (1). a g ð443Þ ¼ 2:303ðA 443 À A 750 Þ 0:1 (1) where A 443 and A 750 are the absorbances measured at 443 and 750e800 nm, respectively. The constant of 2.303 is a conversion factor to convert natural log to the base 10 and 0.1 is the cell path length of the cylindrical cuvette in meters.