Bottle Sampling Depths

by JRMethods

Bottle Sampling Depths, based on downcast profiles

here

The CalCOFI CTD-rosette is equipped with a Sea-Bird Electronic carousel water sampler (SBE 32), a computer-driven, electro-magnetically-released latch system. The 24 ten-liter plastic (PVC) bottles, equipped with epoxy-coated springs & Viton (non-toxic) O-rings, connect to 24 individual triggers by lanyards which keep the bottle ends open. During the downcast, profiles of different sensor measurements vs depth are displayed real-time on a computer screen. Based on the chlorophyll maximum & mixed layer depths, bottles are closed at specific depths to isolate the seawater. The 10 meter bottle spacing shifts up or down (see table below) to resolve steep gradient features such as chlorophyll, oxygen, nitrite maxima and shallow salinity minimum. Salinity, oxygen and nutrients samples are analyzed at-sea for all depths sampled. Chlorophyll-a and phaeopigments samples from the top 200 meters, bottom depth permitting, are also extracted for 24hrs and analyzed at-sea. Most CTD-rosette casts sample 20 depths to a maximum of 515 meters, bottom depth permitting. Occasionally, additional bottle depths or multiple bottles are tripped at the same depth to provide extra water for ancillary projects or primary productivity incubations. Two basin stations, off Santa Monica & Santa Barbara, are sampled beyond 515m to within 10m of bottom. Wire-length permitting, a 3500m deep cast is performed at sta 90.90.

Typical bottle depth spacing based on downcast fluorescence & mixed layer profiles

  CTD Cast Type I CTD Cast Type II Cast Type III
Niskin/Carousel Fluorescence Max Fluorescence Max Fluorescence Max
Position # 0 – 50meters 50 – 120meters > 120meters
1 515 515 515
2 440 440 440
3 380 380 380
4 320 320 320
5 270 270 270
6 230 230 230
7 200 200 195
8 170 165 175
9 140 140 160
10 120 125 150
11 100 112 140
12 85 100 130
13 70 87 120
14 60 75 110
15 50 62 100
16 40 50 80
17 30 40 60
18 20 25 40
19 10 10 20
20 0 0 0
       
  10m bottle spacing 12m bottle spacing 10m bottle spacing
  0 – 70 50 – 125 100 – 160
       
1st Criteria:   Depth of Fluorescence Maximum during CTD Down Cast
2nd Criteria:   Mixed Layer Depth