Table 1.

Substrate additions and 2,4-D mineralization rates in long-term laboratory incubations of surface ice cores from GrIS and estimated 2,4-D degradation potential on the surface of GrIS

Microcosma	No. of days	Amt of 2,4-D added		Amt of 2,4-D mineralized (nmol)	tfdA gene copy no. (104)	2,4-D degradation potential
		dpm	nmol			nmol day−1 m−2	ng C day−1 m−2
1a	133	49,234	1.30	0.17	<1	0.65	16
1b	166	50,338	1.33	0.12	<1	0.38	9.0
1c	206	46,802	1.23	0.13	<1	0.31	7.4
2a	133	49,234	1.30	0.82	<1	3.07	74
2b	166	50,338	1.33	0.53	<1	1.60	38
2c	206	46,802	1.23	0.46	<1	1.12	27
3a	133	49,234	1.30	0.56	<1	2.09	50
3b	166	48,308	1.27	0.35	<1	1.05	25
3c	206	46,802	1.23	0.48	<1	1.16	28
Control a	133	49,234	1.30	0.13	NDb	0.49	12
Control b	166	48,308	1.27	0.14	ND	0.42	10
Control c	206	46,802	1.23	0.11	ND	0.27	6.5
4	451	48,252	1.27	0.22	<1	0.24	5.8
5	451	48,252	1.27	0.51	<1	0.57	14
6	451	48,252	1.27	0.91	<1-1.7	1.00	24
Control (4–6)	451	48,252	1.27	0.25	ND	0.28	6.8
7	451	53,358	1.32	0.29	1.5-3.1	0.32	31
8	451	53,358	1.32	0.13	<1	0.14	13
9	451	53,358	1.32	0.23	<1	0.26	25
Control (7–9)	451	53,358	1.32	0.13	ND	0.15	14

^aa, b, and c, 1st, 2nd, and 3rd additions, respectively.

^bND, not determined.