604 A 0.04 0.02 0.00 ** -0.02 -0.04 * ** 0.00 0.02 0.04 0.06 0.08 0.00 0.01 Absolute sum of the coefficients


FIGURE 5. Results of L1-regularized regression analysis assessing the correlation between environmental predictors and foraminiferal test volume–to–surface area ratio, illustrating the significant association of temperature and oxygen with volume–to–surface area ratio for the Pacific waters with <3 ml/liter [O2] and the significant association of temperature with volume–to–surface area ratio in Pacific waters ≥3 ml/liter [O2]. Bolded black lines and text represent the environmental parameters that comprise the best model for predicting test (log10-transformed) volume–to–surface area ratio for Pacific waters that have <3 ml/liter [O2] (A) and ≥3 ml/liter [O2] (B) based on AIC and BIC model selection criteria (see Table 3). Gray lines and text are environmental predictors not included in the best model. The numbers that lead the environmental predictors rank their relative importance and subsequently correspond to the order in which the predictor variables are added to the model. Dashed vertical lines point to the absolute sum of the coefficients of the environmental predictors that comprise the best-supported model.


foraminifera ranged from 8.99 · 109 to 8.21 · 1010W/kg. We also assume that active transport via cytoplasmic streaming is the dominant mechanism for oxygen transport within the cell. We assign a cytoplasmic streaming velocity of u ~5 · 10−3mm/s (Travis and Bowser 1991) and approximate the density of the cell cytoplasm, r, as 1g/cm3 (Korsun et al. 1998). The energy yield from burning one mole of glucose via aerobic respiration is denoted by the constant q, ~2.08 · 10−6mol/W· s. The volume–to–surface area ratios observed


in our data concur in trend and absolute value with the predictions from equation (2) based on the effects of temperature and dissolved oxygen concentration on organism metabolism (Fig. 6). Contour lines tracing the theoretical maximum test volume–to–surface area ratio, given constant values for the parameters enumerated above, show a trend of increasing test volume–to–surface area ratio with decreas- ing seawater temperature and increasing dissolved oxygen concentration. Oxygen tends


to have a linear effect on the predicted maximum test volume–to–surface area at constant temperature, and supports observa- tions made by Bernhard (1986), whereas temperature exhibits a nonlinear effect. In waters with less than 3 ml/liter [O2], such as those found along the Pacific continental coast of North America, slight changes in dissolved oxygen concentration yield the greatest change in test morphology. In low-oxygen environ- ments, a decrease in the test volume will reduce metabolic demands and an increase in test surface area will maximize the rate of oxygen uptake by the cell via diffusion (Bernhard 1986). Although several Rotallid foraminifera are known to denitrify (Risgaard-Petersen et al. 2006; Piña-Ochoa et al. 2010; Koho et al. 2011; Bernhard et al. 2012) or harbor symbionts (Bernhard et al. 2000, 2001), foraminifera still likely respond to variations in ambient dissolved oxygen concentration because aerobic respiration is energetically favorable over other metabolic strategies (Nardelli et al. 2014). However, in


0.02 0.03 * * * log vol/sa


CAITLIN R. KEATING-BITONTI AND JONATHAN L. PAYNE Pacific <3 ml/L * ** B log vol/sa


3. POC flux 2. Oxygen


4. Calcite 3. POC flux


* ***** ** ** * 4. Calcite


* *


*


* *


*


* *


Pacific ≥3 ml/L


*


Standardized coefficients


1. Temperature


2. Oxygen


1. Temperature


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