Carbon isotopes and concentrations of phytol:
Size-fractionated particle samples were collected using McLane WTS-LV in-situ pumps using four 142-millimeter (mm) diameter filter tiers. Size fractions reported here are as follows: 1.2-6 micrometers (μm) size fraction collected on two pre-combusted, stacked 1.2 μm glass fiber filters and 0.3-1.2 μm size fraction collected on two pre-combusted, stacked 0.3 μm glass fiber filters. Samples were stored at -80 degrees Celsius until processing. Chlorophyll was extracted from frozen or freeze-dried filter splits as part of a total lipid extraction using a mixture of chilled methanol, dichloromethane, and milliQ water (Bligh & Dyer, 1959; Sturt et al., 2004) using freeze/thaw, sonication, and vortexing/shaking to enhance extraction efficiency. Filter material was removed, and the total lipid extract (TLE) was further purified via liquid-liquid extraction against salt water and dried under N2. Lipid classes from each TLE were separated on silica gel mini columns (Bastow et al., 2007); reported here is the sum of the concentrations of phytol from chlorophyll in these fractions and the weighted average d13C value. Lipid classes were aliquoted by volume and saponified to cleave the phytol side chain from intact chlorophyll. Neutral lipids were obtained via liquid-liquid extraction from the basic mixtures and concentrated using a Turbovap evaporator. Quantitative aliquots were derivatized to trimethylsilyl (TMS) ethers and analyzed via gas chromatography mass spectrometry with a TG-5MS column. Samples containing sufficient phytol were analyzed for stable carbon isotope composition via gas chromatography-isotope ratio mass spectrometry equipped with a TG-5MS column. Phytol standards of a known δ13C value were derivatized alongside samples to account for isotope fractionation during the derivatization reaction as well as the δ13C value of added derivative carbon.

Carbon isotopes and bulk particulate organic carbon (POC, d13C POC):
Size-fractionated particle samples were collected using McLane WTS-LV in-situ pumps using four 142 mm diameter filter tiers. Size fractions reported here are as follows: 1.2-6 μm size fraction collected on two pre-combusted, stacked 1.2 μm glass fiber filters and 0.3-1.2 μm size fraction collected on two pre-combusted, stacked 0.3 μm glass fiber filters. Samples were stored at -80 degrees Celsius until processing. Filter splits were then freeze-dried, and carbonates were removed via acidification. Bulk POC concentration and isotope composition were measured using a Thermo Flash elemental analyzer coupled to a Conflo IV and MAT 253 Plus isotope ratio mass spectrometer (EA-IRMS, Thermo Scientific). These data are not blank corrected, but blanks were measured and are negligible relative to measured POC and d13C values.

Amino Acid analysis (d13C THAA):
Size-fractionated particle samples were collected using McLane WTS-LV in-situ pumps using four 142 mm diameter filter tiers. Size fractions reported here are as follows: 1.2-6 μm size fraction collected on two pre-combusted, stacked 1.2 μm glass fiber filters and 0.3-1.2 μm size fraction collected on two pre-combusted, stacked 0.3 μm glass fiber filters. Samples were stored at -80 degrees Celsius until processing. Quantitative splits were freeze‑dried, hydrolyzed, purified, derivatized, and analyzed for nitrogen and carbon isotope composition of individual amino acids. δ13C values of total hydrolysable amino acids (δ13CTHAA) were calculated as in McCarthy et al. (2013): δ13CTHAA = Σ (δ13CAA * mol%AA) where δ13CAA and mol%AA are the δ13C value and the molar percentage contribution of each individual amino acid, respectively. The standard deviation for each sample was calculated as the square root of the weighted average of variances of each individual amino acid.

Trophic Position (TP) from d15N-AA:
Size-fractionated particle samples were collected using McLane WTS-LV in-situ pumps using four 142 mm diameter filter tiers. Size fractions reported here are as follows: 1.2-6 μm size fraction collected on two pre-combusted, stacked 1.2 μm glass fiber filters and 0.3-1.2 μm size fraction collected on two pre-combusted, stacked 0.3 μm glass fiber filters. Samples were stored at -80 degrees Celsius until processing. Quantitative splits were freeze‑dried, hydrolyzed, purified, derivatized, and analyzed for nitrogen and carbon isotope composition of individual amino acids. POM trophic position was calculated from measured δ15N values of glutamic acid+glutamine (Glx) and phenylalanine (Phe) as in Chikaraishi et al. (2009): TP = (δ15NGlx - δ15NPhe - 3.4)/7.6 + 1 . TP propagated uncertainty was calculated as in Jarman et al. (2017).